Question

A true-breeding plant that produces yellow seeds is crossed with a true-breeding plant that produces green seeds. The F1 plants have yellow seeds. What is the expected phenotypic ratio of seed color of the offspring of an F1 × F1 cross?

Answer 1

Answer:

The phenotypic ratio will be 3:1

Explanation:

As per this question there are two phenotypes for seed color, yellow and green. Both the parents are true breeding that means they are homozygous for this trait. Also, all the F1 plants have yellow seed color which clearly indicates that yellow seed color is a dominant trait while green is recessive trait.

The cross of true breeding plants as mentioned above is depicted as under:

Parents                             YY    x   yy

                                          /   \       /   \

F1 generation                Yy   Yy  Yy   Yy

So, as per the law of dominance because of the presence of Y allele, all these progeny will be yellow in color.

Next, when these F1 plants will be crossed, the result will be as under:

F1 generation                    Yy   x    Yy

                                         /   \         /   \

F2 generation               YY   Yy   Yy   yy

The genotypic ratio of F2 generation is 1:2:1

The phenotypic ratio of F2 generation is 3:1

It simply means that in F2 generation, 3 progeny which have allelic combination YY & Yy will be yellow colored while 1 progeny which has allelic combination yy will have green color.