Question

What will be the probable phenotype ratio if a white summer squash (Wwyy) is crossed to yellow summer squash (wwYy)?
(A) two white: two yellow
(B) two white: two green
(C) one white: one yellow: one green
(D) two white: one yellow: one green

Answer 1

Hint: Genetics is a branch of biology which deals with the study of genes, genetic variation and heredity in organisms. Genotype and phenotype are the most frequent using terms in genetics to determine the genetic and physical characteristics. Genotype (genetic characteristics) and phenotype (physical characteristics).
Example: character taken — height, phenotype (tall and dwarf) and genotype (TT, Tt, tt)

Complete answer:
It is the case of dominant epistasis where two genes interact with each other in which one gene suppresses the action of another gene. In the case of summer squash, three types of fruit colour appear: white (W), yellow(Y) and green(y). Here due to the effect of epistasis, white colour fruit (W) is dominant over the other two colours fruit (green and yellow). Y is dominant over y.
 So, W--Dominant-> Y----Dominant--> y
Green fruits produced in recessive condition (wwyy). Genotypes having W, only white coloured fruit will appear. Genotypes having Y, only yellow-coloured fruit will appear. Genotype having both recessive w and y, the green colour will appear.
White summer squash (Wwyy) X Yellow summer squash (wwYy)
Gametes formed are: (Wy), (wy), (wY). Cross is shown in the given Punnett square.

	(wY)	(wY)	(wy)	(wy)
(Wy)	(WwYy) White	(WwYy) White	(Wwyy) White	(Wwyy) White
(Wy)	(WwYy) White	(WwYy) White	(Wwyy) White	(Wwyy) White
(wy)	(wwYy) Yellow	(wwYy) Yellow	(wwyy) Green	(wwyy) Green
(wy)	(wwYy) Yellow	(wwYy) Yellow	(wwyy) Green	(wwyy) Green

   Ratio- eight white: four yellow: four green --->two white: one yellow: one green

So, (D) is the correct option.

Note:
In the above, we detailed the genotype and phenotype of a summer squash fruit. Punnett square is necessary to determine the character of offspring. Hence, from this crossing, we found two white: one yellow: one green ratio.