In Martians there is a genetic condition called silly walk, which is controlled

Question

In Martians there is a genetic condition called silly walk, which is controlled by an autosomal dominant allele with 25% penetrance. In addition to showing incomplete penetrance the allele shows variable expressivity, such that 10% of silly walkers have a slightly silly walk, 60% of silly walkers have a moderately silly walk, and 30% of silly walkers have a very silly walk. If two heterozygotes mate and are expecting their first child, what is the chance that the child has at least one copy of the silly walk allele? 1/2 2/3 0 1/4 1 3/4 If two heterozygotes mate and have one child, what is the chance, if it receives at least one copy of the allele, that it will have a very silly walk? 0.75 times 0.30 0, 25 0.05 0.75 times 0.70 0.25 times 0.30 0.30 0.25 times 0.70

Explanation / Answer

1. if two heterozygotes mate and are expecting their first child, what is the chance that the child has at least one copy of the silly walk allele is 1/2.

2. 0.75 x 0.70

This could occur if both parents were heterozygotes:

2/3 X 2/3 X 1/2 = 4/18 = 2/9

Or if one parent is heterozygous:

2/3 X 1/3 X 1/2 = 2/18 = 1/9

+1/3 X 2/3 X 1/2 = 1/9

= 2/9

Thus the probability is 2/9 + 2/9 = 4/9.

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