Important words and concepts
from Chapter 13, Campbell & Reece, 2002
(1/29/2005):
by Stephen T. Abedon (abedon.1@osu.edu)
for Biology 113 at the Ohio State University
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Course-external links are
in brackets Click [index] to access site index Click here to
access text’s website Vocabulary
words
are found below |
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(1) Chapter title: Meiosis and Sexual Life
Cycles
(a)
[meiosis and sexual life cycles
(Google Search)] [index]
(a)
Genetics is the science of the study of heredity and variation
(b)
[genetics (Google Search)] [index]
(a)
Genes are sections (linear segments) of DNA
(b)
Typically genes specify the construction of specific proteins
(c)
Together these proteins control an organism’s inherited traits
(d)
[genes (Google Search)] [index]
(a)
Genes
have specific nucleotide sequences
(b)
Copies of these sequences are passed from parents to offspring in the
process of heredity
(c)
[heredity (Google Search)] [index]
(a)
The nucleotide sequences of genes can vary
between individuals (even within individuals)
(b)
These sequence variations are also passed on to offspring
(c)
The existence of these alternative nucleotide sequences forms the root
of quite a bit of the phenotypic variation one observes among individuals of
the same species
(d)
[variation genetic (Google Search)] [index]
(a)
A chromosome, within a eukaryotic cell, is
a single double helix
(b)
Eukaryote chromosomes have certain properties
and structures including
(i)
centromeres
(ii)
telomeres at their ends
(iii)
they are linear (rather than closed circular like bacterial
chromosomes)
(iv)
they are propelled to daughter cells during anaphase, etc.
(c)
Note that your text is using the more global definition of chromosome
at this point, i.e., more than just something that is visible during mitosis
(d)
We, however, will tend in this class to employ a more-narrow definition of eukaryotic chromosome, i.e., nuclear DNA-protein complexes that are visible
through a light microscope
(e)
[chromosome (Google Search)] [cytogenetics gallery (Department of Pathology – University of Washington)][index]
(a)
A locus is the actual, physical location of a gene on a chromosome
(b)
[locus genetic, locus chromosome (Google Search)] [index]
(a)
A karyotype is an arrangement of chromosomes, in
order from largest to smallest, on a photographic plate
(b)
Karyotypes separate chromosomes into different types based on
(i)
Size
(ii)
Staining (i.e., banding) patterns
(iii)
location of the centromere (e.g.,
near one end versus near middle)
(c)
See Figure on lower right of
page 234
(d)
[karyotype (Google Search)] [karyotypes links (MicroDude)] [index]
(9) Homologous
chromosomes (homologues)
(a)
A cell that contains two or more of a given type of chromosome is said to contain two or more homologous chromosomes
(b)
Note that homologues are not necessarily identical (i.e., do not
necessarily possess exactly the same nucleotide
sequences, without variation), but do tend to be very, very,
similar
(c)
Alls cells from normal humans contain at least 22 pairs of homologous
chromosomes (cells from human females contain 23)
(d)
[homologous chromosomes,
homologue or homologues
(Google Search)] [index]
(a)
A cell that contains only one of each type of chromosome that is typical for its species is said to be
haploid
(b)
For humans, a haploid cell possesses 23 chromosomes
(c)
That is, a total of 23 distinguishable types of chromosomes
(d)
Another way of saying this is that n = 23
(e)
[haploidy, haploid (Google Search)] [index]
(a)
Most human cells are diploid
(b)
This means that the cell contains two sets of chromosomes, i.e.,
two haploid
sets
(c)
That is, a total of 46 chromosomes
(d)
2n = 46
(e)
These 46 chromosomes are, in turn, distinguishable into 23 pairs of homologues (with one exception, see below)
(f)
[diploidy, diploid (Google Search)] [index]
(a)
The majority of chromosomes in a diploid cell exist,
under all normal circumstances, as one half of a homologous pair
(b)
Such chromosomes are termed autosomes
(c)
Cells from normal humans contain 44 autosomes (male or female)
(d)
[autosome or autosomes
(Google Search)] [index]
(a)
Exceptions to the two-of-each-type-of-chromosome rule are
the sex chromosomes
(b)
In particular, in humans and other mammals the sex chromosomes are
found as a non-homologous pair in males
(c)
That is, a haploid of the chromosome termed X and a
haploid of the chromosome termed Y are found in males
(d)
Females possess a homologous pair of X chromosomes (and hence human
females possess 23 pairs of homologous chromosomes)
(e)
[sex chromosomes (Google Search)] [index]
(a)
Asexual reproduction involves
(i)
No change in ploidy going from parent to offspring
(ii)
Little genetic
variation
between parent and offspring
(iii)
Only mitotic division between parent and offspring
(among eukaryotes at least)
(b)
[asexual reproduction,
asex (not nearly as
popular as "sex" but still a term used by some) (Google Search)] [asexual reproduction biology
(includes a number of plants "doing it") (The Biology File)]
[Human Cloning Foundation (is this for
real?)] [index]
(a)
Sexual reproduction involves
(i)
Changes in ploidy over the course of going from parent to offspring
(ii)
Significant genetic variation between parent and
offspring
(iii)
Both mitotic and meiotic division
between parent and offspring
(b)
[sexual reproduction,
"sex" alone had
nearly 35 million google hits 2/2/2001, over 87 million hits as of 2/13/02, and
about 262 million hits on 2/9/04—that’s an approximate doubling per year! (Google Search)] [index]
(a)
A life cycle is a description of an organism as it passes from
conception to production of progeny (offspring)
(b)
The human life cycle is divided between a somatic stage and a
gamete
stage
(c)
See Figure 13.4, The human
life cycle
(d)
[life cycle (Google Search)] [the haploid-diploid cycle of
sexual reproduction (Access Excellence)]
[index]
(a)
The soma, or somatic cells of a human are mostly diploid (or possess
a higher ploidy)
(b)
These are the cells that constitute the majority of your body
(c)
The evolutionary goal of your soma is the make gametes and then to assure their fertilization and
subsequent development, thereby contributing genetically to the next generation
(d)
[soma cell, somatic cell, somatic cells (Google Search)] [index]
(a)
A minor portion of your somatic cells give rise to your gametes
(b)
These cells are called your germ-line cells
(c)
Note that the majority of your cells are not capable of making gametes,
only cells from your germ line are
(d)
[germ line (Google Search)] [index]
(a)
Gametes are haploid cells
(b)
They are called sperm and ova (coming from the male and the female,
respectively)
(c)
Gametes do not divide
(d)
In humans, gametes are generated by meiosis
(e)
[gamete or gametes (Google Search)] [index]
(a)
All sexual life cycles are characterized by an occurrence of meiosis
(b)
Meiosis specifically converts the diploid stage of an
organism to its haploid stage
(c)
In humans, only germ line cells undergo meiosis
(d)
Anatomically, this occurs in the sperm- or ova-generating testes or
ovaries
(e)
See Figure 13.6, Overview of
meiosis: how meiosis reduces chromosome number
(f)
(below meiosis is considered in greater detail)
(g)
[meiosis (Google Search)] [index]
(a)
Fertilization (a.k.a., syngamy) is also involved in all sexual life cycles
(b)
Fertilization specifically converts the haploid stage of an
organism to its diploid stage
(c)
That is, the haploid to diploid conversion during a life cycle in most
organisms is a result of fertilization
(d)
[fertilization, syngamy (Google Search)] [insemination and fertilization
(The San Francisco Center for Reproductive Medicine)]
[index]
(22) Variety of
sexual life cycles
(a)
The human life cycle is only one of a variety of sexual cycles
(b)
Different sexual life cycles vary in terms of whether haploid
or diploid
(or both) cells undergo mitosis between fertilization and meiosis and fertilization
(c)
In humans (and most though not all other animals) only the diploid
stage is capable of undergoing mitosis; the haploid cells do not divide
(d)
See Figure 13.5a, Three
sexual life cycles in the timing of meiosis and fertilization (syngamy)
(e)
[variety of sexual life cycles
(Google Search)] [index]
(a)
Various fungi, protozoa, and
algae do not undergo mitosis during their diploid stage
(b)
Instead they undergo mitosis only during their haploid stage
(c)
See Figure 13.5b, Three
sexual life cycles in the timing of meiosis and fertilization (syngamy)
(d)
Note that this does not mean that gametes are
replicating
(e)
Instead it means that gametes (i.e., cells capable of undergoing fertilization)
are generated by mitosis rather than by meiosis (that is,
if the immediate cellular parent of a gamete is itself haploid then the gamete
must have been the product of mitosis)
(f)
Depending on the organism, the haploid stage may or may not remain
unicellular, i.e., there exist multicellular haploid organisms
(24) Alternation of generations
(a)
Plants and various species of algae undergo both haploid and diploid
mitosis
(b)
This is termed alternation of generations since both the haploid and
the diploid organisms are considered separate generations
(c)
See Figure 13.5c, Three
sexual life cycles in the timing of meiosis and fertilization (syngamy)
(d)
[alternation of generations
(Google Search)] [index]
(a)
The multicellular diploid organism given alternation of
genertations is termed the sporophyte
(b)
Sporophytes give rise to haploid spores which go on to found the haploid
organism
(c)
[sporophyte (Google Search)] [index]