Genetic linkage mapping for a large number of families ident

Genetic linkage mapping for a large number of families identifies 6% recombination between the genes for blue sclera and exostoses. At the exostoses locus, alleles E and e control the normal and exostoses phenotypes respectively. Allele B producing blue sclera is dominant to the wild type recessive allele b. Jacob and Brittany each have blue sclera, and each lacks exostoses. Jacob’s mother has blue sclera and exostoses, while his father normal sclera and lacks exostoses. Brittany’s father lacks exostoses and has blue sclera, while her mother has exostoses and normal sclera. Which of the following genotypes best describes Brittany?

(a) B E

(b) B e / b E

(c) B/b; e/E

(d) you can’t be certain, but the probability that she is Be//bE is 0.94

(e) you can’t be certain, but the probability that she is Be//bE is 0.47

Solution

The answer is e, because since the exostoses is a dominant trait but when both the alleles are present then only the phenotypes of exostoses is seen. when any of the alleles is missing the condition is normal. In this case, Brittany\'s father lacks exostoses so, he is recessive for exostoses and has blue sclera. His genotype will be BBee or Bbee as the blue sclera is dominant over the recessive. Her mother has exostoses with normal sclera which mean her genotype will be bbEe or bbEe. So the probability of Brittany having blue sclera and lacking sclera is 1/2 which equals to 0.5 when the genotypes of the parents are crossed which is closer to the option e. Brittany will have a copy of dominant allele B with a single allele of either E or e.