1. CHAPTER 8 The 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. Preparation of a karyotype
Fixative
Packed red
And white
blood cells
Hypotonic solution
Blood culture
Stain
White
Blood cells
Centrifuge 3 2 1
Fluid
Centromere
Sister chromatids
Pair of homologous chromosomes 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
Abnormal chromosome count is a result of nondisjunction
Either homologous pairs fail to separate during meiosis I
Nondisjunction in meiosis I
Normal meiosis 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
Normal meiosis I
Nondisjunction in 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
Egg cell
n + 1
Zygote 2n + 1
Sperm cell
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. A man with Klinefelter syndrome has an extra X chromosome
Poor beard growth
Breast development
Under- developed testes
Figure 8.22A

12. A woman with Turner syndrome lacks an X chromosome
Characteristic facial features
Web of skin
Constriction of aorta
Poor breast development
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. Homologous chromosomes
Deletion
Duplication
Homologous chromosomes
Inversion
Reciprocal translocation
Nonhomologous chromosomes
Figure 8.23A, B

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