Question

Which of the following statements can be related to epistasis?
A. It involves two non-allelic pairs of genes
B. One pair of genes masks the effect of another pair of genes
C. Expression of both the dominant and recessive alleles may be suppressed by the epistatic gene
D. All of the above

Answer 1

When one gene tries to mask or hide the action of another non-allelic gene, then this phenomenon is known as epistasis. The gene masking the effect is known as the epistatic gene. The gene whose action is hidden is known as the hypostatic gene.

Complete answer: When any gene situated on one locus suppresses the effect of another gene situated at another locus, then that suppressing gene is called the epistatic gene, and the gene which is being suppressed is called the hypostatic gene. Since both the genes are situated on the different locus, therefore, they are non-allelic pairs of genes. In epistasis one pair of genes masks the effect of another pair of genes. Epistasis is of two kinds. These two types are the recessive epistasis and the dominant epistasis. Recessive epistasis is when the epistatic gene is recessive or epistasis occurs due to the recessive allele. An example of recessive epistasis is the coat colour in mice. In recessive epistasis, the recessive allele in homozygous conditions masks the effect of the dominant allele. Dominant epistasis occurs when the epistatic gene is dominant or epistasis occurs due to the dominant allele. An example of dominant epistasis is the fruit colour in Cucurbita pepo. In dominant epistasis, the dominant allele in homozygous conditions masks the effect of the recessive allele. Therefore, the expression of both the dominant and recessive alleles may be suppressed by the epistatic gene.
Hence, the correct answer is option D.

Note: In recessive epistasis, the phenotypic ratio of a dihybrid cross $9:3:3:1$ is modified $9:3:4$. In dominant epistasis, the phenotypic ratio of a dihybrid cross $9:3:3:1$ is modified $12:3:1$. The genotypic ratio, however, remains the same in both cases.