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Unformatted text preview: 1 Review: •Transmission genetics - what are the general patterns? •Name some factors that can alter Mendel’s ratios of expected offspring phenotypes. •How can we determine whether actual data (observed ratios) fit the expected ratios? Genotype + Environment -> Phenotype Phenotypes are not always a direct reflection of genotypes Siamese cat Himalayan rabbit Why do individuals in this family of Siamese cats show different color patterns? Mechanisms of sex determination • Environmental temperature cues hormone environment • Chromosomal (genetic) presence of sex-determination factor gene number of sex chromosomes • Reptiles have temperature- dependent sex determination (In another of Dr. Crews’ study species, whiptail lizards, all individuals are female.) 2 ! artwe " Table 4.2 Purves Fig. 9.13 1 17 3 Sex chromosomes differ in number between genders. In humans and other mammals, these are the X and Y chromosomes. Hartwell, Fig. 4.3 X Y Humans are diploid. In the human genome, there are 22 distinct pairs of homologous chromosomes, called autosomes. Campbell, fig 15.9 Various systems for genetic determination of sex. As in mammals, the fruitfly Drosophila has distinct X and Y sex chromosomes which determine the individual’s gender....
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- Fall '06