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After Class Practice Set 3 - Q49 and Q51
#1 Posted : Tuesday, June 08, 2021 2:33:02 AM
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Hello! I was wondering if I could get clarification on these 2 questions from the Bio After Class Practice Set 3

Q- 49

I had trouble understanding the reason why the answer is 1/2. I figured that if the father was autosomal dominant for Huntington’s and the mother was assumed to be normal, that the probability of the child getting the disease would be 1/2 (as the mother would always give an unaffected gene but the father could either give a copy of the affected gene or a normal). Why is there a probability that the child will get the disease and also another probability that the disease allele is passed on?

Q 51

This question I was just confused and chose monohybrid cross because I figured that a test cross we cross an individual with a dominant phenotype with a homozygous recessive inidividual to figure out whether the individual is homozygous or heterozygous for the dominant trait. I didn’t think that it would still be considered a test cross if the genotype of the dominant phenotype indiivdual was already known before the cross. Can this be clarified?

Any help is appreciated! :)
#2 Posted : Wednesday, June 16, 2021 4:30:23 PM
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49. There is a one-half probability that the individual will get the disease (Father is Aa) and then there is another half probability that the disease allele will be passed onto the child. ½ x ½ = ¼. Therefore, answer choice B is correct.

51. When the genotype does not equate to the phenotype it can be described as reduced expressivity or penetrance. This eliminates answer choices C and D. The difference between reduced penetrance and reduced expressivity is that penetrance is a description of whether the disease is present or not, while expressivity is a description of the degree of the trait. Therefore, the passage deals with unaffected individuals who carry the Huntington disease allele and penetrance is the best answer. One can think of penetrance of how much the trait penetrates the population to produce affected individuals.
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