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Bellringer Problems: PKU Bellringer Problems: Huntington’s Disease Bellringer Problems:CF Non-Mendelian Genetics Modifications to the expected Mendelian ratios… For example – in snapdragons, cross a red flowered plant with a white flowered plant… Mendel predicted you would end up with… But he was wrong… You get all *pink* flowers! Why? R = red and r = white Red x white Pink x Pink Incomplete Dominance Incomplete Dominance Intermediate phenotype in heterozygotes… It is a “blend” between the dominant and recessive forms of the gene Sample Problem In horses, the dominant D allele allows coat color to fully develop. The d allele dilutes, or weakens, coat color. When a chestnut (brown) horse is crossed with a cremello (nearly white) horse, their offspring are palominos (gold with white manes and tails) Sample Problem Continued What is the genotype of… • A chestnut horse? ______________ • A cremello horse? ______________ • A palomino horse? ______________ What would be the expected phenotypic ratios of a cross between two palomino horses? Another example from your dragons… The case of the missing purebred… Manx cats are born tailless. But if you cross two Manx cats you will never get 100% Manx kittens. Never ever ever. Lethal Alleles Lethal Alleles The homozygous condition is lethal… Sample Problem Achondroplasia, a form of dwarfism, is caused by the dominant allele A. Embryos with the genotype AA do not survive. Suppose that two people with achondroplasia get married and have children. What phenotypic ratio would you observe in the couple’s children? The case of the orange cows… In cattle, red hair is dominant to white hair…but when you cross a red bull with a white cow, you get… ROAN CATTLE Codominance Definition: Codominance • BOTH alleles are expressed at the same time • Heterozygous = both phenotypes expressed equally R = red and R’ = white Red x white Roan x Roan Practice Problem Andalusian chickens – Black feathers is codominant with white feathers – Heterozygous = __________________________ FB = black and FW = white Black x white F BF W x F BF W It’s a guy thing, you wouldn’t understand… Sex-linked Definition: Sex-linked Pattern of inheritance for genes located on X (sex) chromosome. Rarely on Y… Sex-linked Genes Example: Colorblindness XB, Xb, Y Genotypes? Phenotypes? Practice Colorblindness: Normal Male x Carrier Female Genotypes Phenotypes Sex-linked Genes Example: Hemophilia XH, Xh, Y Genotypes? Phenotypes? Practice Hemophilia: Hemophiliac Male x Carrier Female Genotypes Phenotypes Blood Types
