Question

what should you expect to observe if a pea plant that is homozygous dominant for a certain trait is crossed with a pea plant that is homozygous recessive for that trait?

a. all of the plants in the \\(f_1\\) generation will have a combination of the two traits.
b. all of the plants in the \\(f_2\\) generation will have the recessive trait.
c. all of the plants in the \\(f_2\\) generation will have the dominant trait.
d. all of the plants in the \\(f_1\\) generation will have the dominant trait.

Explanation:

Analyze the parental genotypes

The problem describes a cross between a pea plant that is homozygous dominant for a certain trait and a pea plant that is homozygous recessive for that trait. Let the dominant allele be represented by \(T\) and the recessive allele by \(t\).

• Homozygous dominant parent: \(TT\)
• Homozygous recessive parent: \(tt\)

Determine the F1 generation genotype

When these two parents are crossed (\(TT \times tt\)), each parent can only pass on one type of allele to the offspring.

• The homozygous dominant parent passes on the \(T\) allele.
• The homozygous recessive parent passes on the \(t\) allele.
• Therefore, all offspring in the first filial (\(F_1\)) generation will have the heterozygous genotype: \(Tt\).

Determine the F1 generation phenotype

Using the principles of Mendelian Genetics, specifically the law of dominance, the dominant allele \(T\) completely masks the expression of the recessive allele \(t\) in a heterozygous individual.

• Because all \(F_1\) plants have the heterozygous Genotype \(Tt\), they will all express the dominant Phenotype.
• Thus, all of the plants in the \(F_1\) generation will have the dominant trait.

Evaluate the given options

Let's evaluate each option based on our genetic analysis:

• Option A: "All of the plants in the \(F_1\) generation will have a combination of the two traits." This is incorrect because dominance results in only the dominant phenotype being expressed, not a blend or combination.
• Option B: "All of the plants in the \(F_2\) generation will have the recessive trait." This is incorrect; self-crossing \(F_1\) (\(Tt \times Tt\)) yields a \(3:1\) ratio of dominant to recessive phenotypes in the \(F_2\) generation.
• Option C: "All of the plants in the \(F_2\) generation will have the dominant trait." This is incorrect because about \(25\%\) (\(tt\)) will show the recessive trait.
• Option D: "All of the plants in the \(F_1\) generation will have the dominant trait." This matches our analysis perfectly.

Answer:

• (A) All of the plants in the \(F_1\) generation will have a combination of the two traits.
• (B) All of the plants in the \(F_2\) generation will have the recessive trait.
• (C) All of the plants in the \(F_2\) generation will have the dominant trait.
• (D) All of the plants in the \(F_1\) generation will have the dominant trait. (Correct answer)