Question

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.)

Answer 1

Answer:

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.

Answer 2

Answer:

33.3%

Explanation:

Truebreeding organisms refer to organisms that are homozygous for a particular trait and will pass down only one characteristics of a trait to their offsprings. According to the question, a single gene that has two alternative forms called alleles is involved. Thus, a truebreeding parent will be homozygous for either of the two characteristics of a trait.

For example, let's look at the height trait coded for by a height gene that has two alternative forms (alleles) viz: T for tallness and t for shortness, where T is the dominant allele and t is the recessive allele. Therefore, truebreeding parents for both characteristics will possess genotypes TT and tt respectively. They will produce an F1 offsprings that is heterozygous (Tt).

The F1 generation (Tt) is self-crossed to produce an F2 generation that possesses the following genotypes: TT, Tt, Tt and tt.

F2 Offsprings with genotypes TT, Tt and Tt are all phenotypically dominant (tall) while offsprings with tt genotype is phenotypically recessive (short). Among the 3 dominant phenotypes, only 1 of them is homozygous (contain same alleles) for the tall characteristics. Hence, 1/3 of the dominant phenotypes will be homozygous

In percentage, this is 1/3 × 100 = 33.3%