Raj having genotype AaBBCc for skin colour marries Simran having genotype AAbbCc for skin colour. What is the chance that they have a child whose skin colour does not match with either Raj's or Simran's?

Question

Raj having genotype AaBBCc for skin colour marries Simran having genotype AAbbCc for skin colour. What is the chance that they have a child whose skin colour does not match with either Raj's or Simran's? (A) 12.5 % (B) 16.67 % (C) 25 % (D) 50 %

Tardigrade Admin · Accepted Answer

Inheritance of skin colour is polygenic. Three different genes colour this trait. The more number of dominant alleles a person has the darker is his skin. Raj has genotype AaBBCc with 4 dominant alleles. He will produce four types of gametes ABC, ABc, aBC, and aBc. Simran has genotype AAbbCc with 3 dominant alleles. She will produce two types of gametes AbC and Abc. Simran is fairer than Raj. The genotypes of their children can be tabulated as follows:

	ABC	ABc	aBC	aBc
AbC	AABbCC 5 dominant alleles Darker than Raj and Simran	AABbCc 4 dominant alleles Same skin tone as that of Raj	AaBbCC 4 dominant alleles Same skin tone as that of Raj	AaBbCc 3 dominant alleles Same skin tone as that of Simran
Abc	AABbCc 4 dominant alleles Same skin tone as that of Raj	AABbcc 3 dominant alleles Same skin tone as that of Simran	AaBbCc 3 dominant alleles Same skin tone as that of Simran	AaBbcc 2 dominant alleles Fairer than Raj and Simran

Thus two genotypes AABbCC and AaBbcc out of 8 genotypes whose skin colour doesn't match with either Raj's or Simran's. Their probability is

\frac{2}{8} = 25%

Q. Raj having genotype AaBBCc for skin colour marries Simran having genotype AAbbCc for skin colour. What is the chance that they have a child whose skin colour does not match with either Raj's or Simran's?

$12.5%$

$16.67%$

$25%$

$50%$