Question

If the allele for dark-colored hair is dominant over the allele for light-colored hair. Select the correct statement which is least likely to occur.
A. A light-haired couple produces a baby with dark hair
B. A dark-haired couple produces a baby with light hair
C. A light-haired woman and a dark-haired man produce a light-haired baby
D. A dark-haired woman and a light-haired man produce a light-haired baby
E. A dark-haired woman and a light-haired man produce a dark-haired baby

Answer 1

Hint: Mendel’s law of dominance states that the allele that is dominant expresses itself, in heterozygous conditions.

Complete answer: It is mentioned that dark-colored hair is dominant and light-colored hair is recessive. So, according to the law of dominance, the dominant allele will be expressed in both homozygous and heterozygous conditions.
In case both recessive alleles are present in a homozygous condition then in that case only the recessive trait can get expressed. This clearly signifies that the couple can have a dark-haired baby only if one of the parents has the dominant allele, or if both of them have the dominant allele.
This can be proved by carrying out the cross.
The gene for hair color has two alleles, B (dominant) and b (recessive).
If both parents have light-colored hair then, they have two ‘b’ alleles (homozygous condition):

		Parent 1
		B	b
Parent 2	b	Bb	bb
	b	Bb	bb

So, a light-haired couple will always have light-haired children and they can never have a dark-haired baby.

Therefore, the correct answer is option A. A light-haired couple produces a baby with dark hair

Note: It is noteworthy that a light-haired couple will always have a light-haired child, but a dark-haired couple may have both light-haired or dark-haired children.