In humans, the allele for the dimple trait is dominant over the allele for the non-dimple trait, and the allele for the cleft ch
in 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 =
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 =
2 answers:
Answer:
Dimples and a cleft chin = 1/4
No dimples and a non-cleft chin = 1/4
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.
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