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2003sep9lecs1-5PQ - MCB142/IB163 Thomson Practice questions...

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MCB142/IB163, Thomson Mendelian and Population Genetics Sep 9, 2003 Practice questions for lectures 1-5 1.(a). If an albino individual has one albino and one normally pigmented parent, write out the genotypes of the parents (albinism is a completely penetrant autosomal recessive trait). What ratio of albino to normal would be expected among subsequent offspring? (b). If two normally pigmented parents produce an albino offspring, what ratio of albino to normal would be expected among subsequent offspring? 2. Achondroplasia is a form of dwarfism inherited as a simple monogenic trait with complete penetrance. Two achondroplastic dwarfs have a dwarf child and later have a second child who is normal. (a). Is achondroplasia produced by a recessive or dominant allele? (b). What are the genotypes of the two parents in this mating? (c). Write down all possible genotypes that can be produced by such a mating. 3. Mom and Dad both find the taste of a chemical called, phenylthiocarbamide (PTC), very bitter. Of their four children, two find the chemical tasteless. Assuming the inability to taste to be a monogenic and fully penetrant trait, is it dominant or recessive? 4. In Drosophila, yellow body is an X-linked recessive trait (females are XX and males are XY). If a female Drosophila with a yellow body is crossed to a wild-type male, denote the genotypes and phenotypes and their proportions in the F1 males and females, and in the F2 generation formed when the F1 are crossed among themselves. 5. A true-breeding strain of blue-eyed bats is developed. In bats, as in humans, the male is the heterogametic (XY) sex. Males of this true breeding blue eyed strain are mated to females of a true-breeding brown-eyed strain of bats. The F 1 are all brown-eyed. What would be the phenotypes of the F 1 bats in the reciprocal cross (true breeding blue eyed females to true breeding brown eyed males) if: (a). The blue-eyed character is an X-linked recessive? (Show your work) (b). The blue-eyed character is an autosomal recessive? (Show your work) Pedigree problems For all the following pedigree questions, unless otherwise stated, assume: (a) The trait is due to the action of a single gene, which has, for the purposes of our study, only two phenotypically distinguishable alleles (one for the trait, one for wild-type if the trait is rare). Page 1
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(b) The trait shows complete penetrance and there are no age of onset effects, i.e., the trait is expressed at birth. (c) The trait shows uniform expressivity. (d) There are no new mutations in any of the individuals in the pedigrees. (e) Mendelian segregation has occurred. (f) If the trait is rare, assume individuals marrying into the pedigree are not carriers, unless there is evidence from the pedigree to the contrary. (g) For maternally (mitochondria) inherited traits, assume there is no heteroplasmy, i.e., individuals are homogeneous for the mitochondrial variation.
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2003sep9lecs1-5PQ - MCB142/IB163 Thomson Practice questions...

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