2 6. Refer to the pedigree above of a human autosomal trait (i.e., not X-linked)

Question

2 6. Refer to the pedigree above of a human autosomal trait (i.e., not X-linked) to answer the following questions. The roman numerals refer to the generations. Circles are females and squares males. Shaded shapes indicate the person possesses the trait. (A) Is the allele determining the trait of interest dominant or recessive? Explain your reasoning. (B) Using the symbols A and a for dominant and recessive alleles, respectively, what is the genotype individual 1? (C) What is the genotype individual 2? (D) If individual 3 marries a heterozygous man, what proportion of their children is expected to have the trait?

Explanation / Answer

Answer:

6). A). The allele determining the trait of interest is recessive.

If the trait is dominat, without appearance of the trait in the parents, it will not appear in the progeny. But children have the trait though their parents do not have the trait. Hence, the trait is autosomal recessive.

B). Genotype of individual 1 = aa

C). Genotype of individual 2 = Aa

D). aa (3) x Aa (heterozygous man)---Parents

a

A

Aa (Absence of the trait)

a

aa (presence of the trait)

50% of their children is expected to have the trait.

7). A). The pedigree indicates that the trait is most likely inherited as X-linked.

B). The genotype of individual 1 = X+X-

      The genotype of individual 2 = X+Y

      The genotype of individual 3 = X+X-

      The genotype of individual 4 = X-Y

C). X+X- (heterozygous) x (individual 2) X+Y -----------Parents

           

X+

Y

X+

X+X+ (regular daughter)

X+Y (regular son)

X-

X+X- (regular daughter)

X-Y (pointy son)

25% of their children are expected to show this trait.

50% of their sons will have the trait.

a

A

Aa (Absence of the trait)

a

aa (presence of the trait)

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