Important words and concepts from Chapter 15, Campbell & Reece, 2002 (1/29/2005):

by Stephen T. Abedon (abedon.1@osu.edu) for Biology 113 at the Ohio State University

 

Description: google_sm

 

Course-external links are in brackets

Click [index] to access site index

Click here to access text's website

Vocabulary words are found below

 

Description: virus4

 

(1) Chapter title: The Chromosomal Basis of Inheritance

(a)                    [the chromosomal basis of inheritance (Google Search)] [index]

(2) Chromosomal basis for Mendel's laws

(a)                    See Figure, The chromosomal basis of Mendel's laws

(b)                    Note in figure:

(i)                     independent assortment

(ii)                   crossing over

(iii)                 gamete formation

(iv)                 fertilization

(c)                    [chromosomal basis for Mendel's laws (Google Search)] [index]

(3) Genetic recombination (see also genetic recombination)

(a)                    Genetic recombination is the mixing up of mom's and dad's chromosomes during meiosis I to produce genetically unique gametes

(b)                    Two processes contribute to genetic recombination

(i)                     Independent assortment

(ii)                   Molecular recombination

(c)                    [genetic recombination (Google Search)] [index]

(4) Independent assortment (see also independent assortment)

(a)                    Independent assortment is the random sorting of mom's and dad's chromosomes into gametes during anaphase I

(b)                    Recall that tetrads line up in random orientations with regard to the centrosomes during metaphase I

(c)                    Independent assortment is responsible for the progeny distribution following dihybrid crosses as well as the 1:1:1:1 genotypic ratio seen following a two-locus test cross; that is, AaBa x aabb so long as the two loci are found on separate (not the same) chromosomes

(d)                   [independent assortment (Google Search)] [index]

(5) Molecular recombination (see also molecular recombination)

(a)                    Loci found on the same chromosome can be genetically recombined only via molecular recombination

(b)                    This is a consequence of the crossing over observed during prophase I of meiosis (recall our meiosis lab)

(c)                    [molecular recombination (Google Search)] [index]

 

LINKAGE

 

(6) Deviation from expected ratios

(a)                    Given two loci, A and B

(b)                    In the cross AaBb x aabb the expected ratios will be 1:1:1:1 for all possible resulting genotypes

(c)                    A 1:1:1:1 ratio may not be observed if locus A and locus B both reside on the same chromosome

(d)                   See Figure, Evidence for linked genes in Drosophila

(e)                    ["deviation from expected ratios" genetics (Google Search)] [index]

(7) Parental type (see also parental type)

(a)                    Parental types are the parent genotypes participating in a cross

(b)                    I.e., AaBb and aabb are the parental types in the above cross (is this really true or is it more correct to describe the resulting gametes as parental types?)

(c)                    ["parental type" (Google Search)] [index]

(8) Recombinant (see also recombinant)

(a)                    Recombinants are the non-parental-type progeny of a two-locus cross

(b)                    I.e., aaBb and Aabb are the recombinant genotypes (or phenotypes) from the above cross

(c)                    (recall that the cross AaBb x aabb may yield AaBb, Aabb, aaBb, and aabb)

(d)                   See Figure, Evidence for linked genes in Drosophila

(e)                    [recombination (Google Search)] [index]

(9) Linkage (see also linkage)

(a)                    A typical deviation from expected ratios, given two loci on one chromosome, is the occurrence of less than expected numbers of recombinants

(b)                    Such a deviation from expected ratios is termed linkage

(c)                    Linkage means that two alleles found on the same chromosome (i.e., mom's and dad's) tend to be overly represented among progeny

(d)                   This is another way of saying that one may expect an over-representation of parental types

(e)                    Linkage occurs because two loci found on the same chromosome may be separated only via molecular recombination, and molecular recombination is not as efficient a means of genetic recombination as independent assortment

(f)                     [linkage genetic (Google Search)] [index]

(10) Frequency of recombination (see also frequency of recombination)

(a)                    A quantity called frequency of recombination is defined as the number of recombinants divided by the total number of progeny stemming from a single cross

(b)                    Thus, if there are 40 recombinants out of 120 total progeny, then the frequency of recombination is 30% (100 * 40 / 120)

(c)                    See Figure, Recombination due to crossing over

(d)                   The maximum frequency of recombination is 50%--this is what is achieved by two loci present on different chromosomes following independent assortment

(e)                    Complete linkage would show a frequency of recombination of 0%

(f)                     Two loci that are sufficiently separated on a single chromosome are effectively unlinked (though not actually, i.e., chemically so) when the frequency of recombination is 50%

(g)                    This simply means that the two loci are sufficiently separated on the chromosome that crossing over occurs with sufficiently high frequency, between loci, that the efficiency of molecular recombination as a mechanism of genetic recombination approaches the efficiency of independent assortment

(h)                    [frequency of recombination, frequency of recombination problems (Google Search)] [index]

(11) Physical distance analog

(a)                    The efficiency of molecular recombination in unlinking loci is more or less proportional to the physical distance between loci on chromosomes

(b)                    Thus, the greater the frequency of recombination between two loci, the greater the relative linear distance on a chromosome between the two loci

(c)                    Note that different regions of chromosomes molecularly recombine at different rates thus making the translation of frequencies of recombination to actual physical distances imperfect

(12) Genetic mapping (see also genetic map)

(a)                    Frequencies of recombination can be converted into genetic maps

(b)                   See Figure, Using recombination frequencies to construct a genetic map

(c)                    Note that one map unit is equivalent to one percentage point of frequency of recombination

(d)                   Note that >50% frequencies of recombination are produced by adding together smaller frequencies of recombination

(e)                    See Figure, A partial genomic map of a Drosophila chromosome

(f)                     Such maps are called linkage maps

(g)                    They are one means by which human genetic abnormalities, for example, are mapped to specific loci

(h)                    [genetic mapping, linkage mapping, linkage mapping problems, linkage problems genetics (Google Search)] [index]

 

SEX LINKAGE

 

(13) Sex-linkage (X-linkage) (see also sex-linkage and X chromosome)

(a)                    Loci found on the X chromosome are said to be sex-linked

(b)                   See Figure, Sex-linked inheritance

(c)                    Sex-linked loci are also known as X-linked under most circumstances--loci found on the Y chromosome are also sex-linked but are much rarer than loci found on the X chromosome

(d)                   Because males have only a single X chromosome, they are essentially haploid for the X chromosome (hemizygous is the technical term for this)

(e)                    This means that males possessing an X-linked allele will express the phenotype associated with that allele regardless of whether the allele would have been recessive or dominant in the diploid (i.e., female) state

(f)                     This fact impacts the interpretation of pedigrees

(g)                    Consider the following crosses

(h)                    [sex linkage, X linkage, linkage problems sex or X (Google Search)] [index]

(14) XAXA x XaY

(a)                    An affected male mating with a non-carrier female will produce

(i)                     All females as carriers (XAXa)

(ii)                   All males as not affected and not carriers (XAY)

(b)                   See Figurea, The transmission of sex-linked recessive traits

(15) XAXa x XAY

(a)                    A non-affected male mating with a carrier female will produce

(i)                     50% of females that are non-carriers (XAXA)

(ii)                   50% of females that are carriers (XAXa)

(iii)                 50% of males that are non-affected and non-carriers (XAY)

(iv)                 50% of males that are affected (XaY)

(b)                   See Figureb, The transmission of sex-linked recessive traits

(16) XAXa x XaY

(a)                    An affected male mating with a carrier female will produce

(i)                     50% of females that are carriers (XAXa)

(ii)                   50% of females that are affected (XaXa)

(iii)                 50% of males that are non-affected and non-carriers (XAY)

(iv)                 50% of males that are affected (XaY)

(b)                    Note that the presence of the recessive allele by a male parent effectively never impacts on the genotype of sons

(c)                    See Figurec, The transmission of sex-linked recessive traits

(17) XaXa x XaY

(a)                    An affected male mating with an affected female will produce nothing but affected offspring (XaXa and XaY)

(18) Recessive, sex-linked affliction (see also sex-linked recessive)

(a)                    Some relevant afflictions that are both recessive and have sex-linked loci include those which, in the mutant state, result in (need not memorize)

(i)                     Duchenne muscular dystrophy

(ii)                   Some forms of hemophilia

(iii)                 Some forms of color blindness

(b)                    Note that for these or any recessive, sex-linked affliction, males will be much more likely affected than females

(c)                    {For those of you who are mathematically inclined, and want to jump ahead slightly, the frequency of affliction in males is equal to the allele frequency within the population while the frequency of the affliction in females is equal to the square of the allele frequency within the population. That is, for an allele frequency of 0.01 (1%), the likelihood of a male possessing just one allele is 0.01 while the likelihood of a female possessing two such alleles (one on each X chromosome) is 0.01 * 0.01 = 0.0001 (0.01% or one in 10,000)}

(d)                   [recessive sex linked, recessive sex linked problems (Google Search)] [index]

(19) Dominant, sex-linked affliction

(a)                    The converse of the above statement concerning the rate at which males are affected by recessive sex-linked afflictions is, of course, that for any dominant, sex-linked affliction (or wild type phenotype, for that matter), females will be affected at a rate of about 2x that of males (they have two-times as many X chromosomes so are twice as likely to possess an X chromosome possessing the dominant allele)

(b)                    (This would be a rate of affliction of 2 * 0.01 = 0.02 in the above example)

(c)                    [dominant sex linked, dominant sex linked problems (Google Search)] [index]

 

ANEUPLOIDY AND POLYPLOIDY

 

(20) Nondisjunction (see also nondisjunction)

(a)                    When mitosis or meiosis fails to separate sister chromatids or tetrads, this is called nondisjunction

(b)                    Basically, chromosome disjunction fails to occur so sister chromatid pairs are dragged together to one centrosome with neither chromatid dragged to the other centrosome

(c)                    The resulting daughter cells have too many or too few chromosomes

(d)                   See Figure, Meiotic nondisjunction

(e)                    [nondisjunction (Google Search)] [index]

(21) Aneuploidy (see also aneuploidy)

(a)                    A somatic cell that contains too few or too many individual chromosomes is considered to be aneuploid

(b)                    That is, the cell has something to the effect of one extra chromosome or one missing chromosome

(c)                    ["Aneuploidy is the condition of having less than or more than the normal diploid number of chromosomes, and is the most frequently observed type of cytogenetic abnormality. In other words, it is any deviation from euploidy, although many authors restrict use of this term to conditions in which only a small number of chromosomes are missing or added." (General and Medical Genetics)]

(d)                   Typically aneuploidy is an aberrant condition

(e)                    This is due in part to an imbalance in gene expression

(f)                     Typically this imbalance is more anomalous the more genes involved

(g)                    E.g., the bigger the aneuploid chromosome, the worse the effect

(h)                    Contrast aneuploidy with polyploidy (too-many haploid sets of chromosomes) and haploidy (only one haploid set of chromosomes)

(i)                      [aneuploidy (Google Search)] [index]

(22) Trisomy (trisomic) (see also trisomy)

(a)                    An aneuploidy consisting of three copies of one chromosome type is called a trisomy

(b)                    That is, with a trisomy an organism contains one type of chromosome in three copies rather than the expected diploid two

(c)                    Note that the term trisomy is not synonymous to the term triploid (the first represents one extra chromosome while the latter represents one extra haploid set of chromosomes)

(d)                   [trisomy or trisomic (Google Search)] [index]

(23) Monosomy (monosomic) (see also monosomy)

(a)                    An aneuploidy consisting of only a single copy of one chromosome type

(b)                    (instead of the expected diploid two; note, as above, that monosomy is not equivalent to haploidy)

(c)                    [monosomy or monosomic (Google Search)] [index]

(24) Polyploidy (see also polyploidy)

(a)                    An individual that has more than two haploid sets of chromosomes (e.g., 3n, 4n, etc. rather than 2n, the diploid state) is said to be polyploid

(b)                    Triploid (3n) and tetraploid (4n)

(c)                    Polyploidy contributes to less phenotypic aberration than does aneuploidy

(d)                   Polyploidy is common in plants and contributes to plant speciation

(e)                    Some polyploidy occurs in animals but typically this is limited to small patches of tissue

(f)                     [polyploidy (Google Search)] [index]

 

CHROMOSOMAL REARRANGEMENTS

 

(25) Chromosomal rearrangements (see also chromosomal rearrangements)

(a)                    Another way in which chromosome number can partially change involves chromosomal rearrangements

(b)                    In addition, chromosomal rearrangements can change gene orders which can sometimes impact on gene expression

(c)                    Chromosomal rearrangements can be involved in disease processes including birth syndromes and some cancers

(d)                   Types of rearrangements include

(i)                     Deletion (e.g., -=- --> -=)

(ii)                   Duplication (e.g., -=- --> -==-)

(iii)                 Inversion (e.g., -=- --> --=)

(iv)                 Translocation (e.g., -=- + -~- --> -=-~- + -~- or --)

(v)                   Reciprocal translocation (e.g., -==- + -~~- --> -=~- + -~=-)

(e)                    Note that reciprocal translocation is between different types of chromosomes and thereby is not identical to the molecular recombination that occurs normally during meiosis

(f)                     See Figure, Alternations of chromosome structure

(g)                    Chromosomal rearrangements play important roles in molecular and organismal evolution

(h)                    [chromosomal rearrangements (Google Search)] [index]

(26) Deletion (see also deletion)

(a)                    A deletion has occurred when part of a chromosome is removed

(b)                    This can result in loss of genes or parts of genes

(c)                    Deletions tend to be more detrimental the more genes involved

(d)                   [deletion mutation, deletion chromosome (Google Search)] [index]

(27) Duplication (see also chromosomal duplication)

(a)                    A duplication occurs when a section of chromosome is duplicated, with the duplicated part found on the same chromosome

(b)                    Duplications tend to be more detrimental the more genes that are involved

(c)                    [duplication chromosome, deletion chromosomes (Google Search)] [index]

(28) Inversion (see also inversion (chromosomal))

(a)                    An inversion occurs when a section of a chromosome is deleted and replaced with the same section inserted in reverse direction

(b)                    The change in orientation can change the expression of involved genes

(c)                    [inversion chromosome (Google Search)] [index]

(29) Translocation (see also translocation (chromosomal))

(a)                    A translocation occurs when a section of a chromosome is lost from one chromosome and inserted into or onto another

(b)                    This, too, can impact on the expression of involved genes

(c)                    [translocation chromosome (Google Search)] [index]

(30) Reciprocal translocation (see also reciprocal translocation)

(a)                    Reciprocal translocation occurs when two different chromosomes exchange sections

(b)                    (i.e., translocate reciprocally)

(c)                    [reciprocal translocation (Google Search)] [index]

 

DOSAGE COMPENSATION AND BARR BODIES

 

(31) Dosage compensation (see also dosage compensation)

(a)                    How is it that men can survive with only a single X chromosome (an X monosomy)?

(b)                    How is it that women can survive with more than one X chromosome?

(c)                    Typically too many or too few chromosomes are deleterious

(d)                   The answer to these questions are that all but one X chromosome in the cells of individuals is inactivated

(e)                    [dosage compensation (Google Search)] [index]

(32) Barr bodies (see also Barr body)

(a)                    The inactivated X chromosomes are called Barr bodies

(b)                    These X chromosomes are replicated mitotically, and reactivated for meiosis

(c)                    Which X chromosome is inactivated in a woman is determined randomly

(d)                   This inactivation occurs only once the embryo has many cells

(e)                    Once inactivated, the same X chromosome remains inactivated in all descendent cells

(f)                     In women who are heterozygous for a locus found on the X chromosome, this means that some cells will express one allele(s) and other cells will express the other allele(s)

(g)                    Description: bicolor96I.e., women are mosaics as far as the expression of loci found on the X chromosome are concerned

(h)                    Example: calico cat (the cat to the right, in fact, is a calico Persian--note in particular how most of the cat is white upon which are found clonal splotches of color)

(i)                      See Figure, X-inactivation and the calico cat

(j)                      [Barr bodies, Lyon hypothesis (Google Search)] [index]

 

HUMAN CHROMOSOME-NUMBER DISORDERS

 

(33) Human disorders involving changes in chromosome numbers

(a)                    Only certain human aneuploids tend to survive to birth

(b)                    Among those that do and live past the first year include

(i)                     Trisomy 21

(ii)                   Trisomy X (XXX)

(iii)                 XXY

(iv)                 XYY

(v)                   Monosomy X (XO)

(c)                    Translocations can result in surviving partial trisomies (again, the more genes involved, the more severe the consequences)

(d)                   Deletions can result in partial surviving monosomies (ditto)

(e)                    [human disorders involving changes in chromosome number (Google Search)] [index]

(34) Down syndrome (see also Down syndrome)

(a)                    Trisomy 21 produces a condition known as Down syndrome

(b)                    Note that chromosome 21 is the smallest of the autosomes

(c)                    Trisomy 21 is the only human autosomal trisomy which has reasonable viability out of the womb

(d)                   See Figure, Down syndrome

(e)                    [Down syndrome, trisomy 21 (Google Search)] [index]

(35) XXX

(a)                    Females with an extra X chromosome display no phenotypic abnormalities

(b)                    Presumably the extra X chromosome simply becomes an extra Barr body

(c)                    [XXX chromosome (Google Search)] [index]

(36) XXY (Klinefelter syndrome) (see also Klinefelter syndrome)

(a)                    Males with an extra X chromosome are phenotypically more feminine than XY males

(b)                    Such males are typically sterile

(c)                    The name for this syndrome is Klinefelter

(d)                   [XXY chromosome, Klinefelter syndrome (Google Search)] [index]

(37) XYY

(a)                    Males with an extra Y chromosome are nearly phenotypically normal

(b)                    [XYY chromosome (Google Search)] [index]

(38) XO (Turner syndrome) (see also Turner syndrome)

(a)                    This is the only human monosomy which can survive to birth

(b)                    Affected individuals survive, are phenotypically female-like, but do not mature sexually and are sterile

(c)                    The name for this syndrome is Turner

(d)                   [XO chromosome, Turner syndrome (Google Search)] [index]

 

OTHER THAN CHROMOSOMAL DNA SEQUENCE

 

(39) Genomic imprinting

(a)                    Cells can modify DNA in such a way that nucleotide sequence does not change but expression of the sequence does change

(b)                    Often this modification involves methylation of DNA (addition of --CH3 groups)

(c)                    Methylation differs between males and females and can impact on development

(d)                   Consequently, under some circumstances it can matter phenotypically whether an allele is inherited from one's father versus one's mother

(e)                    Such circumstances are rare, however

(f)                     See Figure, Genomic imprinting

(g)                    [genomic imprinting (Google Search)] [index]

(40) Cytoplasmic inheritance (see also cytoplasmic inheritance)

(a)                    Not all of your DNA resides in your nucleus

(b)                    For example, mitochondrial DNA resides in your cytoplasm

(c)                    Such DNA is transmitted only maternally (i.e., none comes from dad)

(d)                   This results in traits associated with mitochondrial alleles being transmitted from mother to all children but from dad to none

(e)                    [cytoplasmic inheritance (Google Search)] [index]

 

(41) Vocabulary [index]

(a)                    Aneuploidy

(b)                    Barr bodies

(c)                    Chromosomal basis for Mendel's laws

(d)                   Chromosomal rearrangements

(e)                    Cytoplasmic inheritance

(f)                     Deletion

(g)                    Deviation from expected ratios

(h)                    Dominant, sex-linked affliction

(i)                      Dosage compensation

(j)                      Down syndrome

(k)                    Duplication

(l)                      Frequency of recombination

(m)                  Genetic mapping

(n)                    Genetic recombination

(o)                    Genomic imprinting

(p)                    Human disorders involving changes in chromosome numbers

(q)                    Independent assortment

(r)                     Inversion

(s)                     Klinefelter syndrome

(t)                     Linkage

(u)                    Molecular recombination

(v)                    Monosomic

(w)                  Monosomy

(x)                    Nondisjunction

(y)                    Parental type

(z)                    Physical distance analog

(aa)                 Polyploidy

(bb)                Recessive, sex-linked affliction

(cc)                 Reciprocal translocation

(dd)               Recombinant

(ee)                 Sex-linkage

(ff)                  Translocation

(gg)                Turner syndrome

(hh)                Trisomic

(ii)                    Trisomy

(jj)                    X-linkage

(kk)                XAXA x XaY

(ll)                    XAXa x XAY

(mm)            XAXa x XaY

(nn)                XaXa x XaY

(oo)                XO

(pp)                XXX

(qq)                XXY

(rr)                   XYY

 

Answer to questions from Chapter 15 (of original 1999 edition of text):

(1)     Same as in text

(2)     Same as in text

(3)     Same as in text

(4)     Same as in text

(5)     Same as #9 in text

(6)     Same as #10 in text

(7)     Same as #11 in text

(8)     Same as #12 in text

(9)     Failure to go through Anaphase separation of haploid sets into separate nuclei; failure of nuclear division

(10) Same as #13 in text

(11) Same as #14 in text

(12) Same as #5 in text

(13) Same as #6 in text

(14) Same as #7 in text

 

 

 

 

(42) Practice questions [index]

(a)                    Name a condition that could result from non-disjunction.

(b)                    Name three general categories (kinds) of chromosomal rearrangements?

(c)                    Why, in terms of gene expression, do Barr bodies exist?

(d)                   What is aneuploidy?

(e)                    Red-green colorblindness is caused by an X-linked allele. Mary's brother is red-green color bind but Mary is not (nor were Mary's mother or father). Mary's husband, Bob, is also red-green color blind. What is the probability that Mary's first daughter will be red-green color blind? (note: this is not a trick question, i.e., such as one asking you to calculate or incorporate calculations of the probability of the child being a girl; the question does not.)

(f)                     Name two syndromes that result from nondisjunctions.

(g)                    When a piece of a chromosome breaks off and reattaches onto a non-homologous chromosome, that kind of chromosomal rearrangement is called a/an __________.

(h)                    How many Barr bodies are found in the nuclei of somatic cells obtained from a guy who has Klinefelter syndrome?

(i)                      Mom's mitochondria are slightly defective in their ability to carry out cellular respiration. Dad's are normal in this regard. What fraction of their children will be neither carriers nor affected by this affliction?

(j)                      Four tomato loci named killer, revenge, storebought, and yummy are found to be linked with the following map units of separation. What is the probable order of these loci on the chromosome?

 

killer

revenge

5

killer

storebought

7

revenge

storebought

11

yummy

storebought

13

revenge

yummy

2

 

(k)                    With apologies to Chelsea, President Clinton possesses an AB chromosome and an ab chromosome (i.e., he is a dihybrid where one chromosome possesses both upper-case alleles and the other chromosome possesses both lower-case alleles; the A and B loci control honesty and marital fidelity, respectively, and all of the considered alleles control these characters codominantly such that an Aa individual is honest only half the time and a Bb individual displays marital fidelity only every-other weekend). The A and B loci are separated by 19 map units. If President Clinton produces 1000 sperm (an off day, he can assure you), then what are the expected genotypes of his gametes as well as the expected number of each genotype among the gametes produced?

(l)                      Imagine that a geneticist has identified two disorders that appear to be caused by the same chromosomal defect and are affected by genomic imprinting: blindness and numbness of the hands and feet. A blind woman (whose mother suffered from numbness) has four children, two of whom, a son and a daughter, have inherited the chromosomal defect. If this defect works like Prader-Willi and Angelman syndromes, what disorders do this son and daughter display? What disorders would be seen in their sons and daughters?

(m)                  A red-green color-blind woman marries a normal-sighted man. What will be the phenotype of their daughters?

(n)                    Distinguish molecular recombination from genetic recombination.

(o)                    The results of a cross between a doubly heterozygous individual and a doubly homozygous-recessive individual are 1000 progeny including examples of individuals possessing the following genotypes: AaBb, Aabb, aaBb, and aabb. Assuming linkage between the loci, if both AaBb and aabb progeny are rare, then what alleles were located on the same chromosomes of the double heterozygote?

(p)                    Three-part question: define genetic recombination and then name the two processes that contribute to genetic recombination.

(q)                    During what phase of meiosis are Mom's and Dad's chromosomes randomly tugged to separate cells?

(r)                     Describe the two parental genotypes involved in a test cross that keeps track of two distinct loci.

(s)                     What is the typical hypothesis proposed as an explanation when a test cross results in less than the expected number of recombinant types (expected meaning as observed by Mendel in his various dihybrid pea crosses)?

(t)                     Two loci that are found on the same large autosome, but at opposite ends, would likely have what frequency of recombination between them?

(u)                    Different regions of chromosomes molecularly recombine at different rates. How does this affect the genetic mapping of a chromosome?

(v)                    What is the frequency of recombination between two loci that are separated by 3 map units?

(w)                  At a given X-linked locus, 0.3 of the alleles in a population code for the wild-type phenotype whereas the other half code for a sex-linked (recessive) form of color blindness (this population presumably is isolated or founded by only a few individuals). What fraction of males in this population would you expect would be phenotypically normal (i.e., wild-type with regard to blood clotting ability)? Bonus question: What fraction of females would you expect to be phenotypically normal?

(x)                    A non-color blind woman's brother is colorblind but both parents have normal vision. What are the odds that the woman's first son will be color blind? Assume X-linkage and that the color blind allele is recessive to the non-color blind dominant.

(y)                    In the previous question, if the first son is color blind, then what is the probability that the second son will also be colorblind?

(z)                    A man and a woman have a large family consisting of 10 children, 5 boys and 5 girls. Three of the girls have green noses and three of the boys have green noses. If green noses are inherited as a sex-linked trait, then what are the nose-color phenotypes of the two parents. What are the genotypes of the two parents? Note that there is more than one possible answer.

(aa)                 When sister chromatid pairs are dragged together to one centrosome (with neither dragged to the other centrosome), this is called meiotic __________.

(bb)                An organism that possesses three haploid sets of chromosomes is called __________. (a description of its karyotype)

(cc)                 Which is likely most disruptive (i.e., would make an organisms most sick) when found in the homozygous state, a chromosomal

(i)                     deletion

(ii)                   duplication

(iii)                 inversion

(iv)                 translocation

(v)                   reciprocal translocation

(dd)               What kinds of chromosomal rearrangements can result in changes in gene regulation?

(ee)                 Ignoring mutational or chromosomal rearrangement events in somatic cells during development, explain how a woman could be color blind in one eye but have normal vision in the other.

(ff)                  Name a viable human monosomy.

(gg)                Under what circumstances would you expect other than a 1:1:1:1 ratio of AaBb, aaBb, Aabb, and aabb among the progeny of a single mating between an AaBb individual and an aabb individual?

(hh)                Given linkage, what do we call the genotype that is underrepresented among progeny?

(ii)                    In a dihybrid cross if there are three recombinant types among a litter of 25, then what is the frequency of recombination?

(jj)                    A linkage group is a set of genes that are physically connected and therefore that are to some degree linked. What is the minimum number of human linkage groups? (ignore the impact of the poor Y chromosome on your answer)

(kk)                Given sex linkage and a family consisting of one affected boy, one affected girl, one phenotypically normal boy, and one phenotypically normal girl, then what are the genotypes of the parents? Is this trait recessive, dominant, or can't you tell?

(ll)                    What is nondisjunction?

(mm)            What is reciprocal translocation?

(nn)                Barr bodies are formed from which human chromosome?

(oo)                Other than Y, the smallest human chromosome is number __________.

(i)                     15

(ii)                   18

(iii)                 21

(iv)                 22

(v)                   23

(pp)                Which are either phenotypically normal or nearly so (circle all that apply).

(i)                     XXX

(ii)                   XXY

(iii)                 XYY

(iv)                 XO

(v)                   YO

(qq)                What is the molecular explanation for the occurrence of 1:1:1:1 genotypic ratios among the progeny of a testcross involving one dihybrid parent?

(rr)                   What is linkage? (not sex linkage)

(ss)                  If the total number of parental types is 53 and the total number of progeny is 72, then what is the frequency of recombination?

(tt)                   Complete linkage results in a frequency of recombination of

(i)                     0%

(ii)                   25%

(iii)                 50%

(iv)                 75%

(v)                   100%

(uu)                In genetic mapping, two loci thought to be found on the same chromosome are found to be unlinked. How can one nevertheless, using crosses and determined frequencies of recombination, still determine a physical distance analog between the two loci?

(vv)                Given sex linkage, a phenotypically normal female carrier, and an affected male, then of eight children, how many would be expect would be affected?

(ww)            What kind of inheritance can one reasonably hypothesize is occurring if females within a population are affected at a rate that is twice that of males?

(xx)                What is nondisjunction?

(yy)                How many chromosomes does a human trisomy possess? (note, a normal human cell has 23 chromosomes per haploid)

(zz)                 Name a viable human monosomy.

(aaa)             Which of the following types of chromosomal rearrangements can give rise to a partial trisomy? Assume that independent assortment occurs after rather than before the occurrence of the chromosomal rearrangement. (circle all that apply)

(i)                     Deletion

(ii)                   Duplication

(iii)                 Inversion

(iv)                 Translocation

(v)                   Reciprocal translocation

(bbb)            How does dosage compensation work in normal human females?

(ccc)             At the level of chromosomes, Down syndrome results from what?

(ddd)          How many Barr bodies do the cells of a man with Klinefelter syndrome possess? What about a normal male?

(eee)             The expression of genes can differ between individuals as a consequence of the methylation of DNA. The process is generally referred to as genomic __________ and can give rise to seemingly bizarre inheritance.

(fff)               How does cytoplasmic inheritance work?

(ggg)            The black and yellow pigments in the coats of cats is controlled by an X-linked pair of alleles. Females heterozygous for these alleles have areas of black and areas of yellow in their coat (called "calico"). A calico cat has a litter of eight kittens -- two yellow male; two black males; two yellow females; and two calico females. Assuming there is a single father for the litter, what is his probable color? Adapted from http://www.ups.edu/faculty/kirkpatrick/bio111/studyquestions/11bgeneticsprobs3.htm

(hhh)            http://www.biology.arizona.edu/mendelian_genetics/problem_sets/Sex_linked_Inheritance/sex_linked_inheritance.html

(iii)                  Under what circumstances will two alleles not be subject to independent assortment?

(jjj)                  Contrast genetic recombination with molecular recombination.

(kkk)            Following a cross, linkage can give rise to __________ than the expected number of recombinant types.

(lll)                  What is nondisjunction?

(mmm)      What is an aneuploidy?

(nnn)            What is the difference between "triploid" and "trisomy"? Please make sure that you unambiguously link concepts with terms.

(ooo)            Name three types of chromosomal rearrangements that are in addition to translations (or reciprocal translocations).

(ppp)            The concept of dosage compensation is intimately linked to the presence of __________ bodies in most of the cells of a karyotypically normal human female.

(qqq)            The only human monosomy that tends to survive to birth gives rise to a suite of symptoms together described as __________ syndrome.

(rrr)                DNA methylation is associated with __________ __________ and often differs between the chromosomes inherited from one's mother versus one's father.

(sss)               Hemophilia in humans is due to an X-chromosome mutation. What will be the results of mating between a normal (non-carrier) female and a hemophilic male?

(ttt)                NOTE: WILL NEED QUESTIONS SIMILAR TO THOSE FOUND IN TEXT

(43) Practice question answers [index]

(a)                    Turner, Down, Klinefelter, etc. syndromes.

(b)                    choices include deletion, duplication, inversion, and translocation, either reciprocal or non-reciprocal for the latter.

(c)                    Either two copies or one copy of the X chromosome would be a normal "dosage", but not both. Barr bodies are inactivated X chromosomes, the inactivation of which assures that all individuals have predominantly only a single active X chromosome.

(d)                   An excess or dearth of one or few chromosome types.

(e)                    The first daughter receives an X chromosome possessing the red-green colorblindness allele from Bob with 100% probability. If Mary is heterozygous at this locus (i.e., a carrier) then the daughter has a 0.50 probability of being red-green color blind. What are the odds that Mary is a carrier? The fact that her brother is red-green colorblind implies that Mary's mother possessed one colorblind allele. As a consequence, Mary is a carrier with 0.5 probability. This means that the probability that her daughter will be afflicted is 0.5 x 0.5 = 0.25.

(f)                     Turner syndrome, Klinefelter syndrome, Down syndrome.

(g)                    translocation.

(h)                    1, i.e., the number of X chromosomes minus one which, for a person with Klinefelter syndrome, is two X chromosomes, so a single Barr body (as opposed to XY males who have no Barr bodies).

(i)                      all will be afflicted though only daughters will also be carriers so the answer is zero.

(j)                      storebought-killer-revenge-yummy

(k)                    AB and ab are the parental types and Ab and aB are the recombinant gametes. 19 map units of separation implies the frequencies of the two latter genotypes will be 19/2 = 9.5%, each, and the two former genotypes will be 81/2 = 40.5%, each. Per 1000, this works out to 405, 405, 95, and 95 gametes for each genotype, respectively.

(l)                      Both children are blind. The son's children will suffer from numbness while the daughter's children will suffer from blindness.

(m)                  Red-green color blindness is caused by a sex-linked recessive allele. Since the daughters will receive an X chromosome from both parents and since one of those chromosomes (the one from the father) will be both wild-type (not color blinding) and dominant, all of the daughters will be carriers possessing the wild-type phenotype (not color blind).

(n)                    Genetic recombination = molecular recombination + independent assortment. It is the mixing up of alleles that came from an organism's mom and dad. Molecular recombination is the crossing over that occurs during prophase I of meiosis.

(o)                    Ab and aB.

(p)                    Genetic recombination is the mixing up of Mom's and Dad's genes; the two processes are independent assortment and molecular recombination

(q)                    Anaphase I

(r)                     AaBa x aabb or AABB x aabb; if you really want to get fancy with your answer, then: A?B? x aabb

(s)                     Linkage

(t)                     50% (i.e., a probability approaching 1.0 of chiasmata formation between the two loci, but an only 0.5 probability of resolution of the crossing over to produce the recombinant-type gametes)

(u)                    Linkage maps produced by frequencies of recombination will be imperfect predictors of the actual nucleotide distance between loci

(v)                    3% frequency of recombination

(w)                  30% of the males would be phenotypically normal, since males have only one X chromosome and half of the X chromosomes in the population would carry the wild-type allele; For females, the calculation is more difficult: A female is normal unless she receives two not-normal alleles; the probability of receiving one not-normal X chromosome is 0.7; By the multiplication rule the odds of receiving two are therefore 0.7 x 0.7 = 0.21; Thus, the odds of not receiving exactly two not-normal alleles are 1 -- 0.21 = 0.79

(x)                    If her brother is color blind then that means that her mother is a carrier. The probability that the woman is also a carrier therefore is 0.5; the probability that her first son will receive the X-chromosome with the color-blind allele is also 0.5; therefore the odds that the first son will be color blind are 0.5 x 0.5 = 0.25

(y)                    If the first son is color blind, then that means that the women is a carrier, thus making the probability that she is a carrier equal to 1.0 (rather than the 0.5 we predicted earlier); the odds that the son will be color blind given that the woman is a carrier, however, remains the same, 0.5: 1.0 x 0.5 = 0.5

(z)                    The mother has a green nose, the father does not; the green-nose allele is dominant to the wild-type allele; the mother is a heterozygote so approximately half of her offspring received the green-nose allele; We know that the father does not have a green nose because not all of the girl progeny have green noses (which they would have to have if the nose-color locus is X-linked); we know that the nose-color allele isn't Y-linked because the girls are affected as well as the boys (and not all of the boys are affected); Alternatively, if the allele is recessive, then the father has a green nose and the mother has a normal-colored nose, but is a carrier.

(aa)                 Disjunction

(bb)                Polyploid

(cc)                 Probably the deletion (a); the rest you might be concerned with gene dosage effects or gene regulation problems, but the deletion represents an actual loss of genetic material

(dd)               Actually, all of them can, but not including translocation and inversion in your list I will count as an incorrect answer

(ee)                 X-linked character; woman is a heterozygote; normal-vision X chromosome was turned in the cell lineage that led to one eye while the color blind-vision X chromosome was turned off in the cell lineage that led to the other eye

(ff)                  XO, i.e., Turner syndrome

(gg)                If there is linkage between the A and B loci

(hh)                Recombinant

(ii)                    100*3/25 = 12 map units = frequency or recombination

(jj)                    23 (i.e., one for each autosome plus the X chromosome)

(kk)                The parents are a heterozygous unaffected mother (XXA) and a hemizygous affected father (XAY); the trait is recessive; the children's genotypes are (in order): XAY, XAXA, XY, and XXA (by the same logic this also works for dominant)

(ll)                    Nondisjunction is the failure during mitosis or meiosis of the separation of sister chromatids during anaphase or anaphase II or the separation of chromosomes from tetrads during anaphase I of meiosis

(mm)            Translocation is the movement of a part of a chromosome onto another, not homologous chromosome (or, at least, not as normal homologous recombination as observed during prophase I of meiosis); in reciprocal translocation the ends of two non-homologous chromosomes are exchanged thereby creating two hybrid chromosomes

(nn)                Barr bodies are formed from the X chromosome

(oo)                (iii) 21

(pp)                (i) XXX and (iii) XYYY

(qq)                Lack of linkage for two loci found on same chromosome or two loci are found on different chromosomes

(rr)                   Linkage is the physical attachment between two different loci requiring recombination for separation of alleles

(ss)                  100* (72 -- 53) / 72

(tt)                   (i) 0%

(uu)                By determining distances between loci located between the two otherwise unlinked loci

(vv)                50%, half the boys and half the girls will be affected (since whether or not a child is affected in this case is a function of which allele they got from their mother, who is heterozygous)

(ww)            Sex-linked dominant

(xx)                Nondisjunction is the accidental increase or decrease (typically by 1) in the number of chromosomes in a cell as a consequence of failure to separate centromeres or tetrads during mitosis or meiosis

(yy)                46 + 1

(zz)                 Turner syndrome (XO)

(aaa)             All but deletion and inversion

(bbb)            Normal human females have one active X chromosome per each of their cells, with the other chromosomes more or less inactivated as a Barr body

(ccc)             Three chromosome 21s

(ddd)          One, zero

(eee)             Imprinting

(fff)               E.g., the DNA carried by mitochondria

(ggg)            The father is yellow: he did not donate any color gene to his sons and donated a yellow color gene to each of his daughters

(hhh)            http://www.biology.arizona.edu/mendelian_genetics/problem_sets/Sex_linked_Inheritance/sex_linked_inheritance.html

(iii)                  When those genes are linked

(jjj)                  Genetic recombination involves both independent assortment and molecular recombination

(kkk)            Lower; less

(lll)                  Nondisjunction is the failure of chromosomes to separate during meiosis (I or II) or during mitosis

(mmm)      An aneuploidy is too many or too few chromosomes within a cell, except too many in full haploid units, in which case we describe these as haploid or polyploid

(nnn)            Triploid is three haploid sets of chromosomes whereas trisomy is one too many of a single chromosome

(ooo)            Deletion, insertion, inversion

(ppp)            Barr

(qqq)            Turner

(rrr)                Genomic imprinting

(sss)               all sons are normal and all daughters are carriers. From http://www.biology.arizona.edu/mendelian_genetics/problem_sets/sex_linked_inheritance/06Q.html.

(ttt)                QUESTIONS FROM TEXT

 

 

 

 

 

 

DELETE ALL OF FOLLOWING WHEN CONVERTING TO HTML:

 

(2003) A man who is red-green colorblind marries a woman who is neither colorblind nor a carrier of the allele for this trait. Which of the following statements would best describe their probable offspring? Recall that red-green color blindness is a sex-linked recessive trait.

(a)    50% of their daughters will be colorblind.

(b)   All of their children will be colorblind.

(c)    All of their daughters will be colorblind.

(d)   All of their sons will be colorblind.

(e)    None of their children will be colorblind.

 

A: (e) None of their children will be color blind; from: http://www.nicholls.edu/biol-ds/biol155/ps/gpr3.htm (chapter 15)

(2003) In Drosophila melanogaster the genes for normal bristles and normal eye color are known to be about 20 map units apart on the same chromosome. Individuals homozygous dominant for these genes were mated with homozygous recessive individuals. The F1 progeny were then test-crossed. If there were 1,000 offspring from the test cross, how many of the offspring would you predict would show recombinant phenotypes?

 

A: (e) 200 (chapter 15)

(2003) A man and a woman have a large family consisting of 12 children, 6 boys and 6 girls. Three of the girls have green noses and three of the boys have green noses. If green noses are inherited as a sex-linked trait, then what are the nose-color phenotypes of the two parents. What are the genotypes of the two parents? Is the green-nose trait dominant or recessive? Note that there is more than one possible answer.

 

A: The mother has a green nose, the father does not; the green-nose allele is dominant to the wild-type allele; the mother is a heterozygote so approximately half of her offspring received the green-nose allele; We know that the father does not have a green nose because not all of the girl progeny have green noses (which they would have to have if the nose-color locus is X-linked); we know that the nose-color allele isn't Y-linked because the girls are affected as well as the boys (and not all of the boys are affected); Alternatively, if the allele is recessive, then the father has a green nose and the mother has a normal-colored nose, but is a carrier. (chapter 15)

(2003) In a plant, leaf color and leaf shape are controlled by two linked genes. Leaves of the wild-type plant are red. A recessive mutation in this gene causes white leaves. Wild-type leaves are pointed, and a recessive mutation in this gene causes them to be smooth. The following crosses were performed:

 

pure breeding white, smooth X pure breeding wild type (i.e., doubly dominant) gives F1: all red, pointed (i.e., doubly dominant)

 

Now, the next cross: red, pointed X pure breeding white, smooth gives F2:


40 white, smooth
36 red, pointed
10 white, pointed
14 red, smooth

 

What is the recombination frequency between the genes for color and for shape?

 

A: (10 + 14)/(40+36+10+14) = 28%; from: http://esg-www.mit.edu:8001/esgbio/mg/linkage.html (chapter 15)

(2003) What are the human phenotypes associated with the following called?

(a)    Trisomy 21: __________

(b)   XO female: __________

(c)    XXY male: __________

 

A: Down syndrome, Turnerís syndrome, Klinefelterís syndrome (chapter 15)

(2003) What is a Barr body?

 

A: A Barr body is an inactivated X chromosome and deals with the problem of dosage compensation since males have only a single X chromosome by females have two (chapter 15)

(2003) Besides cytoplasm (and DNA, transcription, translation, etc.), cytoplasmic inheritance is associated with what?

 

A: mitochondria and chloroplasts (chapter 15)

(2002) Red-green color blindness is X-linked in humans. If a male is red-green color blind, and both parents have normal color vision, then which of the male's grandparents is most likely to be red-green color blind?

(d)   Maternal grandmother

(e)    Maternal grandfather

(f)    Paternal grandmother

(g)   Paternal grandfather

(h)   All grandparents are equally likely

 

A: (b) maternal grandfather (In this problem, an X-linked recessive allele is passed from an affected male, to a daughter who is a heterozygous carrier, and subsequently to an affected grandson; adapted from http://www.biology.arizona.edu/human_bio/problem_sets/human_genetics/01c.html) (chapter 15)

(2002) A true-breeding hot pepper plant of genotype GGDD that produces yellow, round peppers is crossed to a true-breeding hot pepper plant of genotype ggdd that produces green, wrinkled peppers. The F1 progeny are of genotype GgDd and all bear yellow, round peppers. F1 plants were then test crossed to ggdd plants and the following progeny plants were produced:

 

Phenotype (class)

Number

green, wrinkled

175

yellow, round

180

yellow, wrinkled

70

green, round

75

total

500

†(G/g = yellow/green, D/d = round/wrinkled)

 

How many progeny are expected for each phenotype class, assuming independent assortment?

 

A: 125, 125, 125, 125 (from http://mendel.genetics.washington.edu/~mraghu/371B_info.html)

 

In the above question, what is the frequency of recombination?

 

A: 70 + 75 / 500 = 145 / 500 = 29% (chapter 14)

(2002) Determine the sequence of genes along a chromosome based on the following recombination frequencies: A -- C, 20 map units; A -- D, 28 map units; B -- D, 25 map units; B -- C, 33 map units; C -- D, 8 map units.

 

A: B -- D -- C -- A (adapted from your text) (chapter 15)

(2002) Given the following data:

 

         Cross AABB x aabb, then cross the resulting genotype, AaBb, with aabb and get 450 AaBb; 450 aabb; 50 Aabb; and 50 aaBb.

         Cross AACC x aacc, then cross the resulting genotype, AaCc, with aacc and get 490 AaCc; 490 aacc; 10 Aacc; and 10 aaCc.

         Cross BBCC x bbcc, then cross the resulting genotype, BbCc, with bbcc and get 460 BbCc; 460 bbcc; 40 Bbcc; 40 bbCc.

 

What is the order of the A, B, and C loci on the same chromosome?† (modified from http://www.blc.arizona.edu/courses/181LW/guides/17-19problems.html)

A: The A and B loci are 100*(50+50)/(450+450+50+50) = 10 map units apart; the A and C loci are 100*(10+10)/(490+490+10+10) = 2 map units apart; the B and C loci are 100*(40+40)/(460+460+40+40) = 8 map units apart; the order, therefore, is A, C, B (chapter 15)

(2002) If the frequency of recombination between two loci is 13%, then among 500 progeny between a doubly heterozygous individual and a doubly homozygous recessive individual, what number would you expect would have a recombinant phenotype?

 

A: 0.13 * 500 = 75 (chapter 15)

(2002) How does dosage compensation work in normal human females?

 

A: Normal human females have one active X chromosome per each of their cells, with the other chromosomes more or less inactivated as a Barr body (chapter 15)

(2002) Indicate which chromosomes these individuals have an excess of or too few of compared to unaffected individuals of the same apparent gender:

(a)    Turner syndrome: __________ (in excess, or too few?)

(b)   Klinefelter syndrome: __________ (in excess, or too few?)

(c)    Down syndrome: __________ (in excess, or too few?)

 

A: X (too few), X (too many), 21 (too many) (chapter 15)

(2002) What is a chromosomal translocation?

 

A: A chromosomal translation is when a portion of one chromosome is detached and then reattached to a different chromosome (chapter 15)

In a plant, leaf color and leaf shape are controlled by two linked genes. Leaves of the wild-type plant are red. A recessive mutation in this gene causes white leaves. Wild-type leaves are pointed, and a recessive mutation in this gene causes them to be smooth. The following crosses were performed:

pure breeding white, smooth X pure breeding wild type

gives F1: all red, pointed

Now, the next cross:

red, pointed X pure breeding white, smooth

gives F2:
40 white, curly
36 red, pointed
10 white, pointed
14 red, curly

What is the recombination frequency between the genes for color and for shape?

 

This is from: http://esg-www.mit.edu:8001/esgbio/mg/linkage.html

(2001) Given the following data:

 

         Cross AABB x aabb, then cross the resulting genotype, AaBb, with aabb and get 450 AaBb; 450 aabb; 50 Aabb; and 50 aaBb.

         Cross AACC x aacc, then cross the resulting genotype, AaCc, with aacc and get 490 AaCc; 490 aacc; 10 Aacc; and 10 aaCc.

         Cross BBCC x bbcc, then cross the resulting genotype, BbCc, with bbcc and get 460 BbCc; 460 bbcc; 40 Bbcc; 40 bbCc.

 

 

What is the order of the A, B, and C loci on the same chromosome?† (modified from http://www.blc.arizona.edu/courses/181LW/guides/17-19problems.html)

A: The A and B loci are 100*(50+50)/(450+450+50+50) = 10 map units apart; the A and C loci are 100*(10+10)/(490+490+10+10) = 2 map units apart; the B and C loci are 100*(40+40)/(460+460+40+40) = 8 map units apart; the order, therefore, is A, C, B (chapter 15)

() In a plant, leaf color and leaf shape are controlled by two linked genes. Leaves of the wild-type plant are red. A recessive mutation in this gene causes white leaves. Wild-type leaves are pointed, and a recessive mutation in this gene causes them to be smooth. The following crosses were performed:

†pure breeding white, smooth x pure breeding red, pointed

†gives F1: all red, pointed

Now, the next cross:

†F1's red, pointed x pure breeding white, smooth

†gives F2:

†40 white, smooth
†36 red, pointed
†10 white, pointed
†14 red, smooth

What is the recombination frequency between the gene for leaf color and for leaf shape?† (http://biosoft.biosino.org/biobook/mgdir.html)

A: 24 = (10 + 24) / (10 + 24 + 40 + 36) (chapter 15)

 

 

 

 

 

 

From: http://fig.cox.miami.edu/Faculty/Spitze/Fall00/bil250_fall00_pract1.html

18. My friend Larry Weider is green-defective color-blind, which is caused by a recessive sex- linked allele. (He also works on Daphnia.) His wife Nancy is not color-blind. Neither of their two sons Tom and Paul are color-blind. Which of the following statements CANNOT be true?
†A) All of Tom's sons will have normal vision.
†*B) 1/2 of Paul's grandsons will be green-defective color-blind, because they inherited the gene from Paul.
†C) Nancy's mother is colorblind.
†D) None of Nancy's full-sib sisters have color-blind sons.
†E) Nancy's mother's father was colorblind.

 

 

See: http://www.biology.arizona.edu/human_bio/problem_sets/human_genetics/human_genetics.html