Question

Suppose two independently assorting genes are involved in the pathway that determines fruit color in squash. These genes interact with each other to produce the squash colors seen in the grocery store. At the first locus, the W allele codes for a dominant white phenotype, whereas the w allele codes for a colored squash. At the second locus, the allele Y codes for a dominant yellow phenotype, and the allele y codes for a recessive green phenotype. The phenotypes from the first locus will always mask the phenotype produced by the second locus if the dominant allele (W) is present at the first locus. This masking pattern is known as dominant epistasis. what is the expected phenotype ratio for a cross of a green squash with a purebred yellow squash.

Answer 1

Answer:

100% yellow fruit color, Yyww.

Explanation:

Available data:

• two independently assorting genes

• the W allele codes for a dominant white phenotype

• w allele codes for a colored squash

• The allele Y codes for a dominant yellow phenotype

• the allele y codes for a recessive green phenotype

• The phenotypes from the first locus will always mask the phenotype produced by the second locus if the dominant allele (W) is present at the first locus. This masking pattern is known as dominant epistasis

Epistasis means "interruption" and refers to interactions between genes located in different loci in the same chromosome. An “epistatic gene” can alter, influence, or suppress the expression of a "hypostatic gene". When the epistatic gene is dominant, the interaction is known as "dominant epistasis".

W suppresses the expression of Y and y, this means that whenever W is present, the fruit is white. If W is not present, the fruit color can be expressed.

So, the proposed cross in the present problem occurs between a green fruited individual and yellow fruited individual, which suggests that W is absent.

Genotype for Green fruit: yyww

Genotype for purebred Yellow fruit: YYww

Cross:

Parental) YYww    x    yyww

Gametes) Yw  Yw  Yw  Yw  yw  yw  yw  yw

Punnet square)    Yw       Yw       Yw      Yw

                 yw    Yyww  Yyww  Yyww  Yyww

                 yw    Yyww  Yyww  Yyww  Yyww

                 yw    Yyww  Yyww  Yyww  Yyww

                 yw    Yyww  Yyww  Yyww  Yyww

F1) 100% Yellow fruited plants, Yyww

As these two genes assort independently, we can also represent the cross for each gene by separate, like this:

For w gene:

Parental) ww  x  ww

Gametes) w w w w

Punnet square)  w     w

                 w     ww   ww

                 w      ww  ww

F1) 4/4 or 100% colored-fruits

For Y gene:

Parental) YY  x  yy

Gametes) Y Y y y

Punnet square)  Y     Y

                 y     Yy     Yy

                 y     Yy     Yy

F1) 4/4 or 100% yellow fruits, Yy.