Question

A black guinea pig crossed with an albino guinea pig produced twelve black offspring. When the albino was crossed with a second black animal, six blacks and six albinos were obtained. What is the best explanation for this genetic situation?

A- Albino is dominant; black is incompletely dominant.
B- Albino is recessive; black is codominant.
C- Albino is recessive; black is dominant.
D- Albino and black are codominant.

Answer 1

C) Albino is recessive and Black is dominant

Step-by-step explanation:

Alleles are the different versions concerned with a gene. Alleles can be classified to be either dominant or recessive which could be determined by their traits. When alleles are considered dominant is when the traits of an individual has visually one effect from the cross-matching of two versions of alleles. For example, black eyes and brown eyes. Dominant alleles display their effect only when an individual has one copy of the aallele. Here, black eyes are dominant so only one copy of black eyes alleles is needed to have black eyes. But when two alleles are dominant, the result is codominance. Both alleles' effects are equal. Recessive alleles show its effect when a n individual bears two copies of the allele which is also known as homozygous.

Answer 2

C- Albino is recessive; black is dominant

Step-by-step explanation:

The gene involved in this question codes for pigment color in guinea pig. One allele codes for black color (B) and the other codes for albino color (b). According to the question, a black guinea pig when crossed with an albino guinea pig produced all black offsprings. This is because the black allele (B) is dominant over the albino allele (b) i.e. The black allele will always mask the expression of the white allele in a heterozygous state.

This is the case of the first cross. The black and albino guinea pigs were both homozygous i.e. had genotypes BB and bb respectively. Hence, they produced offsprings with a Bb genotype, which is heterozygous. Since B allele (black) is dominant over the albino allele (b), it will cover up the expression of albino color. Hence, all offsprings will appear black.

In the second cross between the same albino guinea pig and another black guinea pig, 6 black and 6 albino guinea pigs were produced. This is because the black guinea pig was not homozygous (BB), it was rather genotypically heterozygous (Bb). Hence it will produce offsprings in a 1:1 ratio consisting of 1 black: 1 albino, which is accurate in this case i.e 6:6 = 1:1