Genetics Q02 Lab Exam I, Summer, 2015 2. Two groups of scientists (1 & 2) are st
ID: 214477 • Letter: G
Question
Genetics Q02 Lab Exam I, Summer, 2015 2. Two groups of scientists (1 & 2) are studying the same species of mammals. Like humans, males are XY and females are XX. Normally the mammals have white colored fur. Each group independently find mutants with brown colored fur and generate true-breeding populations that have only this mutation. Each group knows the mutation maps to an X chromosome and the mutant allele is recessive to white fur. They want to determine if the two mutations are alleles at the same locus. They mate true breeding brown females (group 1) with true breeding brown males (group 2). The scientists determine the two brown mutations represent different genetic loci. Select the data that supports their conclusion. Hint: You might want to write out genotypes to help yourself answer this question. A. All offspring have white fu B. All of the females have white fur and all of the males have brown fur C. 50% of the females and males have brown fur, the other 50 % have white fur D. 50% of the females have white fur, the other 50% have brown fur. All the males have brown fur. E. 50% of the females have white fur, the other 50% have brown fur. All the males have white furExplanation / Answer
Since the question suggests that the mutation is linked to X chromosome. Since the mutation is of recessive type, it will only be expressed in homozygous females. Males having the mutant X chromosome will have the brown fur.
So, a true breeding brown fur having female will have mutated X chromosomes.
If the locus of this mutant allele would have been same then, while formation of gametes from female, crossing over would not eliminate the mutated allele. But here gametes produced from the female is definitely having normal allele because of crossing over (during meiosis), which will lead to development of normal females with white fur but no crossing over happens in males so they all are brown.
Take homozygous female genotype as XwXXwXw which produces 2 normal X containing gamete and 2 mutated X gamete. And gamete from male contains mutant allele. This will give rise to 50% normal white fur having female and 50% will have brown fur.
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