Problem

Solutions For An Introduction to Genetic Analysis Chapter 2 Problem 50P

Step-by-Step Solution

Solution 1

Step #1 of 3

The pedigree is hereditary disorder of the skin:

1 2

1 2 3 4

III

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8 9

a. In this pedigree, we can notice that the affected individual has an affected parent. So, we can say that it is dominant inheritance.

If the trait is recessive, then the first individual in generation 1 should be a carrier to get progeny affected with the disease. Also, in II generation second individual should be a carrier of the recessive allele to get affected offspring and it is the same with 8^th individual in the III generation.

Step #2 of 3

b. Let us say that S is dominant and s is recessive.

Generation I--- genotypes--- s/s, S/s

Generation II-- genotypes--- S/s, s/s, S/s, s/s

Generation III- genotypes--- s/s, S/s, s/s, S/s, s/s, s/s, S/s, s/s

Generation IV-> genotypes--- S/s, s/s, S/s, s/s, s/s, s/s, s/s, S/s, s/s

Step #3 of 3

c. Parents are III-4 and III-5. The cross is between S/s X s/s

The progeny should be S/s, S/s, s/s, and s/s. That is, half of the progeny would be affected and half would not be affected and the probability of having affected child is half and unaffected child is half.

Thus, the chance of having four unaffected children is 1/2 x 1/2 x 1/2 x 1/2 = 1/16.

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