Question

In Summer Squash, the fruit colour can be white, yellow and green. The appearance of white colour is due to a dominant gene W. The latter is
A. Inhibitor gene
B. Complementary gene
C. Epistatic gene
D. Supplementary gene.

Answer 1

Hint: Let’s understand heredity or inheritance first. Heredity refers to the transmission of character from one generation to the next. The gene is the bearer of characteristics. Genes may be dominant or recessive. During inheritance each individual receives two forms of a gene one from each parent. The two forms of the same gene are called alleles.
Alleles of the same gene are the same or different. If the alleles of a gene are different, one allele will be expressed; this gene is called the dominant gene. The effect of the other gene is masked as a recessive gene.

Complete answer:
In the dihybrid crosses with pea plants, Gregor Mendel studied two different genes that controlled two different traits. In this dihybrid cross, each gene locus had an independent effect on a single phenotype. Both the genes do not interact with each other in determining the phenotype. In summer squash, two genes interact to give a third phenotype. This interaction is called epistasis.
In summer squash, three types of fruit colours appear, white, yellow and green. White colour fruit is determined by dominant gene W and its recessive allele is w and yellow colour is controlled by another dominant gene G and its recessive allele is g. In this case an allele (W) at one locus masks the effects of allele (G) on other locus.
A cross between plants having white and yellow fruits produced F1 with white fruits. Inbreeding of F1 plants produced plants with white, yellow and green coloured fruits in F2 in 12: 3: 1 ratio. Here W is dominant to w and epistatic to alleles G and g. Hence it will mask the expression of G and g alleles.

Thus, option C epistatic gene is the correct answer.

Note: When a dominant gene on one locus masks the effect of the other non-allelic gene located on the different locus is called epistasis. In summer squash, the fruit colour may be white, yellow or green due to dominant epistasis.