A black guinea pig crossed with a guinea pig with albinism produced 12 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

This question lacks options, the options are:

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.

The answer is C

Explanation:

This question portrays a cross involving a single gene coding for skin color in guinea pigs. There appears to be two different alleles responsible for this gene: the black allele and the albino allele. According to the question, the first black guinea pig was crossed with an albino guinea pig to produce an all 12 black offsprings while the same albino guinea pig was crossed with another black guinea pig to produce 6 black guinea pigs and 6 albino guinea pigs.

This pattern of genetic inheritance has been explained by Mendel in his law of DOMINANCE, which states that one allele of a gene called DOMINANT allele is capable of masking the expression of another allele called RECESSIVE allele in the heterozygous. Thus, we can say that the black allele is the dominant allele while the albino allele is the recessive allele because in the first cross, the offsprings were all black because the black parent guinea pig is homozygous i.e. same allele, for the black phenotype and hence, the black allele masked the albino allele from the albino parent in the offsprings, thereby, leading to phenotypically black offsprings.

In the second cross, the black parent was heterozygous i.e. contained both black and albino allele in its genotype. Hence, during meiosis, it released a gamete with the albino allele that formed an albino phenotype when it fused with another albino allele from the albino parent.

In a nutshell, the black allele is DOMINANT over albino allele, because it can cover up its expression in a heterozygous state, as seen in the 12 offsprings of the first cross and in the genotype of the second black parent.