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Question

Which of the following statements is accurate when crossing a homozygous dominant parent with a heterozygous parent for any given trait?

Choose TWO correct answers.

25% of the offspring will be homozygous recessive.

75% of the offspring will be homozygous dominant.

100% of the offspring will show the dominant phenotype.

All of the offspring will show the recessive phenotype.

None of the offspring will show the recessive phenotype.

Answer 1

When crossing a homozygous dominant parent (AA) with a heterozygous parent (Aa), the genotypes of the offspring can be determined. The possible combinations are as follows:

• The homozygous dominant parent (AA) can only pass on the dominant allele (A).
• The heterozygous parent (Aa) can pass on either the dominant allele (A) or the recessive allele (a).

The possible offspring genotypes are:

1. AA (from A from homozygous parent and A from heterozygous parent)
2. Aa (from A from homozygous parent and a from heterozygous parent)

This results in:

• 50% AA (homozygous dominant)
• 50% Aa (heterozygous)

Now, evaluating the statements provided:

1. 25% of the offspring will be homozygous recessive. - This is false (0% will be homozygous recessive).
2. 75% of the offspring will be homozygous dominant. - This is false (only 50% will be homozygous dominant).
3. 100% of the offspring will show the dominant phenotype. - This is true (both AA and Aa express the dominant phenotype).
4. All of the offspring will show the recessive phenotype. - This is false (none of the offspring will show the recessive phenotype).
5. None of the offspring will show the recessive phenotype. - This is true (all offspring will show the dominant phenotype).

The correct answers are:

• 100% of the offspring will show the dominant phenotype.
• None of the offspring will show the recessive phenotype.