Biol1107 Unit 4: Genetics 21)The pedigree at the right shows inheritance of a di
ID: 302152 • Letter: B
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Biol1107 Unit 4: Genetics 21)The pedigree at the right shows inheritance of a disease (shaded) controlled by a single gene with two alleles (A/a, or XA/Xa). Filled symbols represent affected individuals. The disease is rare and individuals marrying into the family are unlikely to have a diseased allele. What is the most likely mode of inheritance? a) What are the genotype(s) of the individuals indicated in the chart at the right? b) Individual Genotype II-2 What is the probability that a 4th child of couple III-4 and III-5 will NOT have the disease? c) IV-1 If individual III-9 had a child with a woman not carrying the trait, what would be the probability that the child would have the disease? 22)The pedigree at the right shows inheritance ahodo controlled hy a singleExplanation / Answer
a) This is a case of sex-linked (X-linked) recessive inheritance on the basis of the following discussion:
1. Affected females come from affected father
2. Sons of affected females are affected
b) II-2 is XaYA because if it was homozygous recessive than all the females in the following generation would have been affected. Likewise, III-4 is XAYa for the same reason. III-5 is XaXA because all the females to which III-5 is the mother are not affected.
c) The probability of being a boy or girl is 1/2, and the probability of being affected is Since the father is heterozygous XaYA as determined above and the mother is heterozygous and the mother is heterozygous, the probability of being affected for any child is 1/2.
d) Since neither of the parents is affected, and the father of the male parent is also unaffected, the probability of their child affected is zero.
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