Exam 5 Review: Chapter 27 Meiosis
meiosis - The special two-stage process (meiosis I & II) of nuclear and cytoplasmic divisions, with no DNA synthesis in between them, in sexually reproducing organisms which reduces the number of chromosomes in reproductive cells from diploid to haploid, leading to the production of gametes; each division has four phases: prophase, metaphase, anaphase, and telophase. [Note: Meiosis in males and females is illustrated below.] [Visit the Meiosis Tutorial for some good animations.]
primordial germ cells - The most undifferentiated stem cell in the line leading to gametes; the oogonium in females and the spermatogonium in males.
gametes - The reproductive cells produced by meiosis in the gonads, having the haploid number of chromosomes (mature sperm in males and mature eggs in females), and capable of fusing with a gamete of the opposite sex to produce the fertilized egg = zygote.
zygote - The single diploid cell formed by the successful union of two gametes, sperm and egg, during reproduction before cleavage begins; a fertilized ovum or egg.
haploid - Having a single complete set of chromosomes; the same number of sets of chromosomes as a germ cell or half as many chromosomes as a somatic cell; in humans, only the cells produced by meiosis during gamete formation.
diploid - Having a pair of each type of chromosome; the same number of sets of chromosomes as a somatic cell or twice as many chromosomes as a germ cell; in humans, all cells except those produced by meiosis during gamete formation.
homologous chromosomes = homologues - Each pair of similar DNA molecules, present in diploid cells, containing the same gene sequences (although the individual alleles may vary), each DNA molecule derived from one parent. [Visit What Our Chromosomes Can Tell Us for more information.]
autosomes - Those homologous chromosome pairs which is not sex chromosomes, i.e., not significantly involved in sex determination of the individual; in humans there are 22 pairs of autosomes and one pair of sex chromosomes, the X and Y.
sex chromosomes - The homologous chromosome pair which is not grouped with the autosomes; the homologous chromosome pair which is involved in sex determination of the individual; in humans there are 22 pairs of autosomes and one pair of sex chromosomes, the X and Y; the presence of a Y chromosome determines maleness.
X chromosome - One of the sex chromosomes, the larger of the two, and present in one copy in normal males and in two copies in normal females.
Y chromosome - One of the sex chromosomes, the smaller of the two, and present in one copy in normal males and absent in normal females.
Sketch and label:
1. mitotic cell division.
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2. meiotic cell division.
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| Mitosis | Meiosis |
| (1) a single nuclear division and a single cytoplasmic division
(2) DNA duplicated before the process begins (3) two daughter cells produced (4) progenitor and daughter cells have diploid chromosome number (2N) (5) spindle fibers separate and move chromosomes to daughter nuclei (6) four stages observed in the nuclear division: Prophase - Anaphase - Metaphase - Telophase (7) observed in all somatic cells capable of reproduction (8) there is no opportunity for chromosomes to undergo synapsis nor for crossing-over (recombination of genetic material) |
(1) two nuclear divisions and, usually, two cytoplasmic divisions
(2) DNA duplicated before the process begins (3) four daughter cells produced (4) progenitor has diploid chromosome number (2N) while daughter cells have haploid chromosome number (1N) (5) spindle fibers separate and move chromosomes and chromatids to daughter nuclei (6) four stages observed in each of the two nuclear divisions: Prophase - Anaphase - Metaphase - Telophase (7) observed only in stem cells involved in reproduction of gametes (8) there is an opportunity for chromosomes to undergo synapsis in division I and it is possible for crossing-over (recombination of genetic material) to occur |
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