preworksheet3 - Genome 371, Spring, 2008 Quiz Section 3....

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Genome 371, Spring, 2008 Quiz Section 3. Genotype Phenotype: Cat coat color genetics Goal : To integrate concepts of gene expression (week 1) and inheritance (week 2); to practice predicting phenotypes resulting from multiple genes. Background . The genetics of coat color in cats and other furry mammals is complex. During development of the embryo, melanoblasts (precursors to melanocytes, the melanin-producing cells) migrate in a dorsal-to-ventral direction from the neural crest, and end up in the skin (among other targets). This migration is controlled by at least two genes (w and s). Once they arrive at their destination, melanoblasts differentiate into melanocytes and can start pigment production, the pattern and location of which depends on other genes (such as A , C , B , D , O , etc.). The mechanism of action of these genes is still being worked out and in some instances may shed light on human diseases such as Hirschsprung disease and Waardenburg syndrome (consult the OMIM website for more information about these or other human genetic disorders). In this quiz section you will examine the coats of cats with respect to certain features such as color, pattern, and texture, and deduce as much as you can about the underlying genotypes. The brief guide below takes you through what goes into pigment production and the genes involved in that process. Coat color W or w. W is called the “dominant-white” gene. Before melanocytes can start making fur pigment, they must migrate to the skin. Melanocytes make it to the skin only in ww (homozygous recessive) animals. In W ? animals, the skin lacks melanocytes and the cat is a solid white color (W is completely dominant to w). The dominant white phenotype masks (is epistatic to) other pigment traits. For your information only—don’t memorize! The white gene is also known as c-kit . The normal c-kit protein (made by allele w ) is a melanoblast cell-surface receptor. When the receptor receives a signal in the form of a ligand (called Steel
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preworksheet3 - Genome 371, Spring, 2008 Quiz Section 3....

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