BIS101-001 Midterm1A key

BIS101-001 Midterm1A key - BIS101-001(Chan Winter 2008...

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BIS101-001 (Chan) Winter 2008 Midterm 1, Version A (green) Answer Key 1. You have mutations in seven different genes ( E, N, Z, B, A, W, D ) and performed a number of two-point crosses to construct a genetic map. The data, in map units, are given below. E - N 6 N - W 14 Z - W 2 A - B 3 D - B 11 E - W 8 N - E 6 Z - A 50 A - D 8 E - Z 10 N - A 50 Z - D 50 N - D 50 Z - B 50 N - B 50 A. (5 pts) Draw a line diagram illustrating the genetic map. Include the distance between each adjacent pair of genes. B - 3 - A - 8 - D N - 6 - E - 8 - W - 2 – Z B. (4 pts) How many chromosomes are involved? Can this question be answered with certainty? Explain your reasoning. This question cannot be answered with certainty. BAD and NEWZ each form one linkage group. The data do not allow you to distinguish whether they derive from one chromosome, separated by a large region resulting in 50% recombination, or whether they constitute two different chromosomes. 2. Coat color in cattle is determined by the S locus, which can have different alleles. S produces a band of white around the animal. sh produces a pattern of regular spots. sc produces a uniform color, and s produces large, irregular shaped spots. These 4 alleles form a hierarchy in their dominance (a > b means a dominant to b): S > sh > sc > s . Your uncle Herb is a cattle breeder, and he likes cattle with regular spots, because they sell at a higher price. He wants to purchase a bull that is homozygous for the allele determining regular spots and asks you for help. A. What is the genotype of the desired bull? (2 pts) Desired bull is sh sh. B. How can you determine, which bull to select? Which crosses would you perform and what would be the predicted outcome? (6 pts) Testcross with ss cow (irregular spotted phenotype) because bull with regular spots can be sh sh, sh sc, or sh s.
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1. sh sh x s s --> all sh s regular spots 2. sh sc x s s --> 1/2 sh s regular spots 1/2 sc s uniform color 3. sh s x s s --> 1/2 sh s regular spots 1/2 s s irregular spots Could also testcross to uniform colour cow, who will be either sc sc or sc s . For sh sh homozygous bulls, all progeny will be regular spotted. Bulls that are sh sc or sh s will yield uniform or irregular spotted progeny when crossed to sc sc or sc s cows. To get full credit, answer must state 1) homozygous sh sh bull gives 100% regular spotted progeny in testcross 2) heterozygous sh sc or sh s bull gives some uniform or irregular spotted progeny in testcross. 3. Consider the following pedigree of a rare disease and answer the following questions. A. (5 pts) What is the most likely mode of inheritance, and why? Autosomal recessive. Two unaffected parents have an affected child, so it must be recessive. Affected are females, X-linked recessive traits are much more common in males. B. (5 pts) What is the probability of the child (IV.1) to be affected? Explain your answer.
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