You have an f2 generation derived from two true-breeding parents with different characteristics for the same trait (determined by two alleles of a single gene). what percentage of the f2 generation with a dominant phenotype would you expect to be homozygous for the allele of interest? (hint: the parental cross results in the f1 generation. two f1s are crossed to get the f2 generation.)

The percentage of the F2 generation with a dominant phenotype that would be expected to be homzygous for the allele of interest would be 33.33%

Let us assume that the allele of interest is A, the alternate form would be a.

Starting with true-breeding parents of different characteristics of the same trait:

                          AA   x    aa

                      Aa   Aa   Aa   Aa

All the F1 offspring would be Aa.

Advancing the cross to F2:

                     Aa    x   Aa

                  AA   Aa   Aa   aa

3/4 (AA and 2Aa) of the F2 offspring are with the dominant phenotype. However, only 1 out of the offspring is homzygous.

Thus, if the total of the F2 offspring with the dominant phenotype is 100%, the percentage with homzygous alleles can be calculated as:

                1/3 x 100% = 33.33%

More on monohybrid crossing can be found here: link

The percentage for the homozygous dominant trait would be 25%. in the F2 generation.

Explanation:

Suppose true-breeding parents with the different alleles for the same trait are TT (dominant) and tt (recessive) than the cross of these parents will produce gametes T, T and t, t respectively.

These gametes will form offspring ultimately. Produced offspring will be TT (homozygous dominant), Tt (heterozygous dominant), Tt (heterozygous dominant) and tt (homozygous recessive).

Thus, the percentage of dominant homozygous phenotype in F2 would be 25% in respect of the dominant allele which is TT.

hope this !

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