5 What is the probability that will be affected if the shade

5. What is the probability that will be affected if the shaded symbols represent individuals afflicted with an autosomal recessive trait? Assume that individuals with no family history of the condition are not heterozygous. Hint: There are nine combinations. (12 points) 26 20 22 23 25 30 32 33 34 30 37 28 29 38

Solution

An affected female must be homozygous recessive and must pass one disease allele to each one of her children.

Males are hemizygous for an X-Linked trait. An affected male must have a single disease allele.

A parent with a single disease allele has a probability of ½ of passing the allele to any one of its children.

The probability affected with an autosomal recessive trait must be 25%.