Meiosis Chapter 10.
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Transcript of Meiosis Chapter 10.
Meiosis
Chapter 10
Chromosome Number
Homologous: chromosomes that are passed on from parents 1 from mom/1 from dad
Diploid: cell that contains both sets of homologous chromosomes 2 complete sets of genes # chromosomes in diploid cells written
as “2N” (Human 2N = 46)
Chromosome Number (con’t)
Haploid: cell that contains only 1 set of chromosomes (gamete) Written as “N” (Human N=23) Gametes: reproductive cells (sperm &
eggs) When gametes are formed, contain
only 1 set of chromosomes
Meiosis
Def: The process by which the # chromosomes in a cell is cut in half, and homologous chromosomes are separated
2 Stages: Meiosis I Meiosis IICreates 4 haploid cells (gametes), all
genetically different
Meiosis I
Interphase I (before Meiosis): DNA replicates during S phase Makes 2 new chromatids (copies)
connected by a centromere Occurs in 4 steps: 1) Prophase I:
Each chromosome pairs with homologous chromosome & forms a tetrad
Meiosis I (con’t)
Sometimes when tetrads form, crossing-over can occur
Crossing Over: when homologous chromosomes exchange portions of themselves
Results in new combinations of genes, different from parents
Prophase I
Meiosis I (con’t)
2) Metaphase I: Spindle fibers attach and
chromosomes line up 3) Anaphase I:
Fibers pull homologous chromosomes apart
4) Telophase I: Cytokinesis occurs Results in 2 new diploid (2N)
“daughter” cells
Meiosis II Chromosomes DO NOT DUPLICATE again
(no Interphase) Occurs in 4 steps: 1) Prophase II:
From Meiosis I, have 2 diploid (2N) daughter cells
Meiosis II 2) Metaphase II: Chromosomes line up in center of
cell (just like Metaphase I)
3) Anaphase II: Fibers pull chromatids apart
Meiosis II
4) Telophase II: Nucleus forms around each set
chromatids Cytokinesis occurs Results in 4 haploid (N) daughter cells
(gametes)
Mitosis vs. Meiosis
Mitosis → 2 genetically identical diploid (2N) cells Used for cell growth and replacement
Meiosis → 4 genetically different haploid (N) cells Used for reproduction & formation on
gametes