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?

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.

erinna erinna · Answer 2 · 2021-12-10T11:35:16+01:00

The expected phenotypic ratio of seed color of the offspring of an F1 × F1 cross - 3:1

According the given information:

F1 plants have yellow seeds which means yellow color is dominant over green color.
Let assume Y is allele for dominant trait and y is recessive trait allele
Parent genotype would be:

P1: YY - yellow seeds

P2: yy - green seeds

This is explained by Punnett square:

y y

Y Yy Yy

In F1plants the genotype is Yy
Phenotypically it is yellow because yellow is dominant over green.

The cross of F1 x F1

Y y

Y YY Yy

y Yy yy

phenotypic ratio = 3:1 (Yellow seed : Green seed)

genotypic ratio = 1:2:1

Thus, The expected phenotypic ratio of seed color of the offspring of an F1 × F1 cross - 3:1

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