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 Syncytium: a cell with two or more nuclei Red: chromosome Green: spindle fibers

Fig Checkpoints help regulate the cell cycle

Fig Meiosis Reduction division Equational division

Fig. 4.13a Prophase I in meiosis Chromosome 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 Male donkey: 31 autosomes Female horse:32 autosomes Hybrid animal: mule

Fig Meiosis contributes to genetic diversity 2 13 =10 7

Gametogenesis (gamete formation) Germ cells (embryonic germ cells) mitosis Primary cells (diploid) meiosis gametes differentiation

Primary oocytes Oogenesis: asymmetric meiotic division 500,000 diplotene Diploid germ cells (oogonia) at metaphase II

Male germ cells Meiosis I Meiosis II 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 X-linkage explains the inheritance of alleles of the white gene Criss-cross inheritance: The male inherit their eye color from their mothers, and vice vesa.

Fig Nondisjunction 1/2000 1/2000, W+ male; w female Cytologically with two X chromosomes

Fig Sex chromosome-linked disease Red-green color blindness (recessive) 8% man, 0.44% women Maternal grandfatehr 50% grandson

Fig 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