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CHAPTER 8 The Cellular Basis of Reproduction and Inheritance

CHAPTER 8 The Cellular Basis of Reproduction and Inheritance. Modules 8.19 – 8.23. ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE. 8.19 A karyotype is a photographic inventory of an individual’s chromosomes.

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CHAPTER 8 The Cellular Basis of Reproduction and Inheritance

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  1. CHAPTER 8The Cellular Basis of Reproduction and Inheritance Modules 8.19 – 8.23

  2. ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE 8.19 A karyotype is a photographic inventory of an individual’s chromosomes • To study human chromosomes microscopically, researchers stain and display them as a karyotype • A karyotype usually shows 22 pairs of autosomes and one pair of sex chromosomes

  3. Fixative Packed red And white blood cells Hypotonic solution Blood culture Stain White Bloodcells Centrifuge • Preparation of a karyotype 3 2 1 Fluid Centromere Sisterchromatids Pair of homologouschromosomes 4 5 Figure 8.19

  4. 8.20 Connection: An extra copy of chromosome 21 causes Down syndrome • This karyotype shows three number 21 chromosomes • An extra copy of chromosome 21 causes Down syndrome Figure 8.20A, B

  5. The chance of having a Down syndrome child goes up with maternal age Figure 8.20C

  6. 8.21 Accidents during meiosis can alter chromosome number Nondisjunctionin meiosis I • Abnormal chromosome count is a result of nondisjunction • Either homologous pairs fail to separate during meiosis I Normalmeiosis II Gametes n + 1 n + 1 n – 1 n – 1 Number of chromosomes Figure 8.21A

  7. Or sister chromatids fail to separate during meiosis II Normalmeiosis I Nondisjunctionin meiosis II Gametes n + 1 n – 1 n n Number of chromosomes Figure 8.21B

  8. Fertilization after nondisjunction in the mother results in a zygote with an extra chromosome Eggcell n + 1 Zygote2n + 1 Spermcell n (normal) Figure 8.21C

  9. 8.22 Connection: Abnormal numbers of sex chromosomes do not usually affect survival • Nondisjunction can also produce gametes with extra or missing sex chromosomes • Unusual numbers of sex chromosomes upset the genetic balance less than an unusual number of autosomes

  10. Table 8.22

  11. Poor beardgrowth • A man with Klinefelter syndrome has an extra X chromosome Breastdevelopment Under-developedtestes Figure 8.22A

  12. Characteristicfacialfeatures • A woman with Turner syndrome lacks an X chromosome Web ofskin Constrictionof aorta Poorbreastdevelopment Under-developed ovaries Figure 8.22B

  13. 8.23 Connection: Alterations of chromosome structure can cause birth defects and cancer • Chromosome breakage can lead to rearrangements that can produce genetic disorders or cancer • Four types of rearrangement are deletion, duplication, inversion, and translocation

  14. Deletion Duplication Homologouschromosomes Inversion Reciprocaltranslocation Nonhomologouschromosomes Figure 8.23A, B

  15. A chromosomal translocation in the bone marrow is associated with chronic myelogenous leukemia • Chromosomal changes in a somatic cell can cause cancer Chromosome 9 Reciprocaltranslocation Chromosome 22 “Philadelphia chromosome” Figure 8.23C Activated cancer-causing gene

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