Wooly, sheep-like, hair is a rare dominant trait among people of Scandinavian de
ID: 166717 • Letter: W
Question
Wooly, sheep-like, hair is a rare dominant trait among people of Scandinavian descent. A male with this trait, whose mother had straight hair, moves to an island inhabitated by people not of Scandinavian descent. Assuming no other Scandinavian immigration occurs, what is the probability that a great-grandchild of this male will have wooly hair? If there are eight such great-grandchildren, what is the probability that one will have wooly hair? You may nd pedigree diagrams to be a useful component of your answer. Again, show the logic of your work clearly and concisely.
Explanation / Answer
Given that wooly hair is a dominant trait and the mother had straight hair (meaning the individual is heterozygous). Also, given that no other Scandinavian immigration occurs. To get to the answers, we need to make one more assumption that no inbreeding occurs i.e. none of the great grandchildren are inbred.
The genotype of immigrant is Ww and the rest of the population is ww (where 'W' denotes wooly hair and 'w' denotes normal hair).
Since the island population has only normal hair, and no inbreeding occurs, the heterozygous individuals will produce heterozygous and homozygous recessive progeny in 1:1 ratio.
Immigrant
Child
Grandchild
Great Grandchild
Ww
Ww
Ww
Ww
ww
ww
ww
ww
ww
ww
ww
ww
ww
ww
ww
Hence, the probability that a great-grandchild of this male will have wooly hair is (1/8) 12.5%. If there are eight such great-grandchildren, the probability that one will have wooly hair is 12.5×8 = 100%.
Immigrant
Child
Grandchild
Great Grandchild
Ww
Ww
Ww
Ww
ww
ww
ww
ww
ww
ww
ww
ww
ww
ww
ww
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