1Biology 20 Cell Division – Meiosis Meiosis: Homologous chromosomes: Diploid: Haploid: Gamete: Zygote: Meiosis – The Process: Two phases: 1) Meiosis I Reduction division: 2) Meiosis II Interphase:2MEIOSIS I: Prophase I: Synapsis: Crossing over: Chiasmata (chiasma): Results in: Metaphase I: Metaphase plate: Independent assortment: 2n Æ 223 => Anaphase I: What separates? Sister chromatids are? Telophase I & Cytokinesis: Results in: Are these cells diploid or haploid? MEIOSIS II: No interphase Æ No DNA replication3Prophase II: Metaphase II: What lines up on the metaphase plate? Anaphase II: What separates? Telophase II & Cytokinesis: Results in: Are these cells diploid or haploid? Spermatogenesis: Oogenesis: Before birth till puberty: Puberty: Fertilization: Karyotype (Fig. 8.19): Allows:4Accidents during meiosis: Nondisjunction (Fig. 8.21 A & B): If nondisjunction occurs, gametes result in either: n + 1 = n - 1 = If a (n + 1) or (n - 1) gamete unites with a normal gamete, the resulting zygote (Fig. 8.22): Trisomy (2n + 1): Monosomic (2n – 1): During which meiotic phase would nondisjunction occur? What is trisomy 21? Why is it believed that females tend to contribute more to chromosomal abnormalities than males? Why is there a greater incidence of Downs babies with older females than younger ones? Birth defects & cancer are the result of? Chromosomal alterations include: Deletions: Duplications: Inversions: Translocations: If nondisjunction occurs on the sex chromosomes, it can lead to: XXY = Klinefelter's syndrome => 1:2000 XYY = Normal male => 1:2000 XXX = Metafemale => 1:1000 XO = Turner syndrome =>
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