Question

An allele is dominant if it is expressed in

• A. both homozygous and heterozygous states
• B. second generation
• C. heterozygous combination
• D. homozygous combination.

Answer 1

The Correct Option is A

The question asks about the conditions under which an allele is considered dominant. This is a fundamental concept in genetics.

In genetics, an allele is a variant form of a gene. Humans and many other organisms have two alleles for each gene, one inherited from each parent. These alleles can be the same (homozygous) or different (heterozygous).

An allele is termed dominant if its traits are expressed when at least one copy is present in the gene pair. This means that the dominant allele can manifest its trait in the following genotypic combinations:

1. Homozygous Dominant: This occurs when two copies of the dominant allele are present (e.g., AA).
2. Heterozygous: This occurs when one copy of the dominant allele and one copy of a recessive allele are present (e.g., Aa).

For an allele to be expressed in both the homozygous and heterozygous states, it must be dominant. In contrast, a recessive allele only expresses its trait in the homozygous recessive condition (e.g., aa).

Let's evaluate the options:

• Both homozygous and heterozygous states: This is correct for a dominant allele, as it is expressed in both AA and Aa.
• Second generation: This option does not specify any particular genetic condition relevant to dominance.
• Heterozygous combination: While a dominant allele is expressed in the heterozygous combination, it is also expressed in the homozygous condition, making this option incomplete.
• Homozygous combination: This encompasses both homozygous dominant (AA) and doesn’t necessarily indicate dominance since it doesn't include heterozygous states.

Therefore, the correct answer is: both homozygous and heterozygous states.