In Martians there is a genetic condition called silly walk w

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

Solution

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.