Question

In humans, the allele for the dimple trait is dominant over the allele for the non-dimple trait, and the allele for the cleft chin trait is dominant over the allele for the non-cleft chin trait. Mr. Smith has heterozygous alleles for both traits and exhibits dimples and a cleft chin. Mrs. Smith does not have dimples, nor does she have a cleft chin. The alleles for dimples are D and d, and the alleles for cleft chin are C and c.

What is the probability that Mr. and Mrs. Smith’s child will have the following phenotypes?

Dimples and a cleft chin =

No dimples and a non-cleft chin =

Answer 1

Dimples and a cleft chin = 1/4

No dimples and a non-cleft chin = 1/4

Step-by-step explanation:

This question involves two distinct genes; one coding form dimples and the other for cleft chin. The allele for dimples (D) is dominant over the allele for non-dimples (d) while the allele for cleft chin (C) is dominant over the allele for non-cleft chin (c).

According to the question, Mr. Smith has heterozygous alleles for both traits i.e. combination of both alleles for present (DdCc) and exhibits dimples and a cleft chin. Mrs. Smith, on the other hand, does not have dimples, nor does she have a cleft chin. This means that she can exhibit this trait only when homozygous recessive.

Mr Smith (DdCc) and Mrs. Smith will produce gametes during meiosis as follows:

DdCc- DC, Dc, dC, dc

ddcc- dc, dc, dc, dc

Using these gametes in a punnet square, 16 possible offsprings will be produced in a genotypic ratio 4:4:4:4 = 1:1:1:1.

An offspring with dimples and a cleft chin will possess dominant alleles for both genes. Hence, the probability of having such offspring from a cross is 4/16 or 1/4

The genotype of an offspring with no dimples and no cleft chin is ddcc. Hence, the probability of having such offspring is 4/16 or 1/4.

Answer 2

Probability of Dimples and a cleft chin among their offspring = 1/4

Probability of no dimples and a non-cleft chin = 1/4

Step-by-step explanation:

the allele for the dimple trait D is dominant over the allele for the non-dimple trait d.

the allele for the cleft chin trait C is dominant over the allele for the non-cleft chin trait c.

Mr. Smith has heterozygous alleles for both traits.

Mrs. Smith does not have dimples, nor does she have a cleft chin

Mr Smith DdCc x. ddcc

Probability of Dimples and a cleft chin among their offspring = Dd x dd = 1/2

Cc x cc = 1/2 = 1/2*1/2 = 1/4

Probability of no dimples and a non-cleft chin = Dd x dd = 1/2, Cc x cc = 1/2 = 1/2*1/2 = 1/4.