CO 04

The chromosome theory of inheritance

Fig. 4.5

Metaphase chromosome can be classified by centromere position

Fig. 4.6

Karyotype of a human male

Metaphase chromosomes

Table 4.1

Human: Y makes the difference.

Drosophila: ratio of number of X chromosome to copy number of autosome

Mentally retarded

Y is necessary for male fertility

Fig. 4.7

Mitosis Ensures that Every Cell in an Organism Carries the Same chromosomes

Fig. 4.8

Fig. 4.9

Fig. 4.10

Syncytium: a cell with two or more nuclei

Red: chromosomeGreen: spindle fibers

Fig. 4.11

Checkpoints help regulate the cell cycle

Fig. 4.12

Meiosis

Reduction division

Equational

division

Fig. 4.13a

Prophase I in meiosisChromosome condensation

Pairing of homologous chromosomes

Reciprocal exchange of the genetic information

tetrad

Fig. 4.13d

Fig. 4.13b

Meiosis I: metaphase

Chiasma ensures proper segregation of homologous chromosomes

Fig. 4.13e

Meiosis I

interphase

Fig. 4.13c

Meiosis II

Fig. 4.13f

Meiosis II

Segregation during meiosis

Segregation error: trisomies

trisomy 21: Down syndrome

extra X : Klinefeller male

Nondisjunction

Fig. 4.16

Male donkey: 31 autosomes

Female horse:32 autosomes

Hybrid animal: mule

Fig. 4.17

Meiosis contributes to

genetic diversity

213=107

Gametogenesis(gamete formation)

Germ cells(embryonic germ cells)

mitosisPrimary cells

(diploid)

meiosisgametes

differentiation

Primaryoocytes

Oogenesis: asymmetric meiotic division

500,000

diploteneDiploid germ cells (oogonia)

at metaphase II

Male germ cells

Meiosis I

Meiosis II

20 days 20 days 20 days

mitosis

Spermatogenesis: symmetric meiotic division

Validation of chromosome theory of inheritance

1. The chromosome theory correlates Mendel’s law with chromosome behavior during meiosis.

2. The transmission of particular chromosomes coincides with the transmission of specific traits

Fig. 4.20

X-linkage explains the inheritanceof alleles of the white gene

Criss-cross inheritance:The male inherit their eye color from their mothers, and vice vesa.

Fig. 4.21

Nondisjunction

1/2000

1/2000, W+ male; w femaleCytologically

with two X chromosomes

Fig. 4.22

Sex chromosome-linked disease

Red-green color blindness (recessive)

8% man, 0.44% women

Maternal grandfatehr 50% grandson

Fig. 4.23

Five properties of X-linked recessive disease:

1. More male than female.2. Never pass form father to son (son only get Y from father).3. Maternal father pass the disease to grandson.4. The disease often skip one generation from grandfather through a carrier

daughter.5. With the rare affected female, all her son will be affected and all her daughter will be carriers.

性聯遺傳低磷酸佝僂症

1. More female than male have the disease

2. Father to daughter

3. 50% of son and daughter

Sex-limited trait:Affect a structure or process that is found in one sex but not the other.

Sex-influenced traits:Show up in both sex, but expression of this trait differ between two sex because of hormone difference

- pattern baldness