Meiosis Chapter 11-4

11-4 Meiosis VIII. Chromosome Number A. Homologous Chromosomes Paired chromosomes with genes of same traits in same order 2. Not always identical B. Haploid 1. Gamete cell has one of each kind of chromosome 2. n C. Diploid 1. Chromosome appear in pairs (2 sets of chromosomes 1 from mom and 1 from dad) 2. 2n

A. Occurs in specialized cells that produce gametes IX. Meiosis A. Occurs in specialized cells that produce gametes 1. Gamete = sperm/ovum B. Organisms inherit a single copy of every gene from each parent C. Produces gametes with only 1 set of genes D. Two divisions 1. Meiosis I and Meiosis II 2. Diploid (2n) cell at beginning of Meiosis I and 4 haploid (n) cells at the end of Meiosis II

a. DNA replicates E. Stages Interphase I 1. Interphase 2. Meiosis I Prophase I a. Prophase I - Chromosomes pairs with its corresponding homologous chromosome (matched gene by gene = TETRAD) - Non-sister chromatids overlap & exchange material = Crossing Over (Page 324)

b. Metaphase I - Paired homologous chromosomes line up across center of the cell Metaphase I c. Anaphase I - Homologous chromosomes separate by fibers and move to opposite ends of the cell Anaphase I

d. Telophase I and Cytokinesis - Nuclear membranes form and cell separates Telophase I *The two cells produced by meiosis I have chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I. e. The two cells enter a second meiotic division.

Telophase I and Cytokinesis Page 324 Meiosis I Interphase I Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis

- Chromosomes line up in the middle of the cell 3. Meiosis II a. Prophase II - Spindle fibers forms Prophase II Metaphase II b. Metaphase II - Chromosomes line up in the middle of the cell

c. Anaphase II - Centromere splits sister chromatids and go to opposite ends of the cell Anaphase II Telophase II d. Telophase II and Cytokinesis - Nuclei reform, spindle fibers break down, cytoplasm divides e. END RESULT: 4 haploid cells (different)

Telophase II and Cytokinesis Page 325 Meiosis II Telophase I and Cytokinesis I Meiosis II Telophase II and Cytokinesis Prophase II Metaphase II Anaphase II

X. Gamete Formation A. In male animals, meiosis results in four equal-sized gametes called sperm.

B. In many female animals, only one egg results from meiosis B. In many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction.

XI. Comparing Mitosis and Meiosis Mitosis vs Meiosis 2 divisions 1 division 4 different haploid cells 2 identical diploid cells ½ the # of chromosomes as parent cell Same # of chromosomes as parent cell Sex cells (gametes) Body cells (skin, muscle,..etc.)

Comparing Mitosis and Meiosis prophase (I) metaphase (I) anaphase (I) telophase (I) End of Meiosis I N = 2 2N = 4 End of Meiosis II

A. Chromosomes are groups of linked genes 11-5 Linkage and Gene maps XII. Gene Linkage A. Chromosomes are groups of linked genes B. Chromosomes assort independently not the genes C. Crossing over sometimes separates genes on chromosomes = Genetic Diversity XII. Gene Maps A. Shows distance between genes on chromosomes

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