Bio for non- majors 5

Bio for non- majors 5 - • Nondisjunction during meiosis...

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Mitosis Somatic cells vs. gametes Somatic cells All of the cells in an organism except gametes Diploid (double set of chromosomes) Gametes Reproductive cells (sex cells) Egg or sperm Haploid (single set of chromosomes) Meiosis A single diploid cell divides to produce 4 haploid reproductive cells Meiosis I Meiosis II Figure 10.2a The Steps of Meiosis Sources of Genetic Variation during Meiosis Crossing Over During Prophase I Non-sister chromatid homologous chromosomes exchange reciprocal portions of themselves Independent Assortment During Metaphase I Random alignment of maternal and paternal homologous chromosomes leads to their random distribution Crossing Over during Prophase I Independent Assortment during Metaphase I Sex determination Females: XX Males: XY Sex Outcome in Human Reproduction Spermatogenesis Oogenesis Figure 10.8 Big Difference in Size
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Unformatted text preview: • Nondisjunction during meiosis • Nondisjunction: the failure of chromosomes or chromatids to move to opposite poles during meiosis. • Nondisjunction can occur during Meiosis I or Meiosis II • Syndromes that result from nondisjunction during Meiosis Nondisjunction of autosome – Trisomy 21 (Down Syndrome) • 3 copies of chromosome 21 • Associated with impairment of cognitive ability and physical growth Nondisjunction of sex chromosome – Klinefelter Syndrome • XXY • Male genitalia, no sperm, slight enlargement of hips and breast – Turner Syndrome • X_ • Female genitalia, underdeveloped breast and ovaries Key Points • Meiosis vs. Mitosis • Stages of Meiosis • Sources of genetic variation during meiosis • Spermatogenesis vs. Ooogenesis • Nondisjunction...
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