Question

biol 221 lab 3, 10 points your name__ date__ (c) another form of deafness is caused by a rare autosomal recessive gene. in a mating involving a deaf man and a deaf woman, could some of the children have normal hearing? explain your answer. 4) below is a pedigree of a fairly common human hereditary trait where the boxes represent males and the circles represent females. shading symbolizes the abnormal phenotype. given that one gene pair is involved, (a) is the inheritance pattern x - linked or autosomal, recessive or dominant? (b) give the genotype of each individual in the pedigree. if more than one genotypic possibility exists, present all possible alternatives. 5) in the mouse, gene a allows pigmentation to be deposited in the individual coat hairs, while its allele a prevents such deposition of pigment, resulting in an albino. gene b gives agouti (wild - type) fur, while its allele b gives black fur. (a) diagram the cross between a doubly heterozygous agouti mouse mated with a doubly homozygous recessive white mouse. (b) what would be the expected phenotypic ratio in the progeny?

Explanation:

Step1: Analyze deaf - ness inheritance

Let the recessive allele for deafness be \(a\). A deaf man and a deaf woman are both \(aa\) (since it's autosomal recessive). When they mate, all of their offspring will have the genotype \(aa\) because \(aa\times aa\) only produces \(aa\) offspring. So, none of the children can have normal hearing.

Step2: Analyze pedigree inheritance

(a)

1. If it were X - linked recessive, an affected male would pass the mutant allele to all his daughters. But we see unaffected daughters of affected mothers, so it's not X - linked recessive.
2. If it were X - linked dominant, an affected father would pass the mutant allele to all his daughters and an affected mother would pass it to half of her sons and daughters on average. This doesn't match the pattern, so it's not X - linked dominant.
3. Since males and females are affected in similar proportions and there is no clear X - linked pattern, it is autosomal. And since affected individuals can have unaffected parents, it is recessive.

(b)

Let the normal allele be \(A\) and the mutant allele be \(a\).

• Affected individuals have genotype \(aa\).
• Unaffected parents of affected individuals must be carriers (\(Aa\)). Unaffected individuals with no affected parents or offspring can be either \(AA\) or \(Aa\).

Step3: Analyze mouse cross

(a)

A doubly heterozygous agouti mouse has genotype \(AaBb\) and a doubly homozygous recessive white mouse has genotype \(aabb\).
The cross is \(AaBb\times aabb\).
The gametes produced by \(AaBb\) are \(AB, Ab, aB, ab\) and the gametes produced by \(aabb\) are \(ab\).

(b)

Using a Punnett - square or the product rule:
The possible genotypes and phenotypes are:

• \(AaBb\) (agouti): \(\frac{1}{4}\)
• \(Aabb\) (black): \(\frac{1}{4}\)
• \(aaBb\) (albino): \(\frac{1}{4}\)
• \(aabb\) (albino): \(\frac{1}{4}\)

The phenotypic ratio of agouti : black : albino is \(1:1:2\).

Answer:

• For the deaf - ness question: No, all children will be deaf as both parents are \(aa\) and can only pass on the \(a\) allele.
• For the pedigree question: (a) Autosomal recessive. (b) Affected individuals: \(aa\); Unaffected parents of affected: \(Aa\); Other unaffected: \(AA\) or \(Aa\).
• For the mouse cross question: (a) Gametes of \(AaBb\) are \(AB, Ab, aB, ab\) and of \(aabb\) is \(ab\). (b) Agouti : black : albino = \(1:1:2\)