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Meiosis Chapter 10. Chromosomes  Genes are located on chromosomes inside the cell nucleus  When offspring are formed, 1 set of chromosomes from each.

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Presentation on theme: "Meiosis Chapter 10. Chromosomes  Genes are located on chromosomes inside the cell nucleus  When offspring are formed, 1 set of chromosomes from each."— Presentation transcript:

1 Meiosis Chapter 10

2 Chromosomes  Genes are located on chromosomes inside the cell nucleus  When offspring are formed, 1 set of chromosomes from each parent is passed on

3 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)

4  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 genes

5 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 II Creates 4 haploid cells (gametes), all genetically different

6 Meiosis I  Interphase I: chromosomes replicate, making 2 new chromatids (copies) connected by a centromere  Occurs in 4 steps:  1) Prophase I: Each chromosome pairs with homologous chromosome & forms a tetrad

7 Meiosis I  Sometimes when tetrads form, crossing-over can occur  Crossing Over: when homologous chromosomes exchange portions of themselves  Results in new combinations of genes

8 Meiosis I 22) Metaphase I: Spindle fibers attach and chromosomes line up 33) Anaphase I: fibers pull homologous chromosomes apart 44) Telophase I: cytokinesis occurs; results in 2 new diploid (2N) “daughter” cells

9 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  2) Metaphase II: Chromosomes line up in center of cell (just like Metaphase I)

10  3) Anaphase II: fibers pull chromatids apart  4) Telophase II: cytokinesis occurs; results in 4 haploid (N) daughter cells

11 Gamete Formation  Male Animals: 4 haploid gametes all become sperm  Female Animals: 4 haploid gametes become 1 egg and 3 polar bodies (not used)

12 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

13 Linkage and Gene Maps  Thomas Morgan (1910): discovered many traits inherited together i.e.: fruit fly’s red eyes and mini wings Genes can be placed in “linkage groups” “Linkage Group” = chromosome  Mendel just happened to study genes on different chromosomes

14  T. Morgan: genes on same chromosome should be inherited together Chromosomes = group of linked genes  Chromosomes assort independently; not individual genes

15  However, crossing-over may “unlink” some genes Farther apart = more likely to separate  This action creates new combinations of alleles → more genetic diversity

16 Gene Mapping  Rate which genes become separated and recombine is measured  Describes the relative location of each known gene on a chromosome  Created by “mapping” genes relative locations


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