Question

In summer squash fruit color exhibits epistatsis. There are two genes that affect the color, W and G, and each has two alleles one dominant and one recessive. White color is caused by the dominant W allele. This allele is epistatic to G; that is, any squash with a W allele is white, regardless of the genotype for G. If and only if the fruit is homozygous ww, then G_ produces a green fruit and gg produces a yellow one. Assume you have a white squash of genotype (WwGg) which you mated with green squash of genotype (wwGg). Fill out the Punnet square below and then predict the phenotypic ratio in the offspring.

4x4 Punnet Square

Answer 1

Answer:

• 8/16 White fruits

• 6/16 Green fruits

• 2/16 Yellow fruits

Explanation:

Parental genotypes:           WwGg                  x                    wwGg

Gametes)                     WG   Wg   wG   wg                  wG    wG    wg    wg

Punnet Square

                                          WG            Wg           wG            wg          

                          wG        WwGG      WwGg      wwGG       wwGg

                          wG        WwGG      WwGg      wwGG       wwGg

                          wg         WwGg      Wwgg       wwGg       wwgg

                          wg         WwGg      Wwgg       wwGg       wwgg

F1 Genotypic proportions:    2/16 WwGG

                                                   4/16 WwGg

                                                   2/16 Wwgg

                                                   2/16 wwGG

                                                   4/16 wwGg

                                                   2/16 wwgg

F1 Phenotypic proportions:    

• 8/16 are White fruits: 2/16 WwGG, 4/16 WwGg, 2/16 Wwgg. As W suppresses the expression of G or g, whenever W is present (as WW or Ww), the fruit color is white.

• 6/16 Green fruits:  4/16 wwGg, 2/16 wwGG.

• 2/16 Yellow fruits: 2/16 wwgg.

As ww does not suppress the expression of G or g, whenever ww is present, the fruit color might be green (wwGG or wwGg) or yellow (wwgg).