An allele is dominant if it is expressed in

The correct option is A

Both homozygous and heterozygous states

The correct option is A:

Explanation of the correct option:

1. An allele is one of several gene types that can appear at the same time on a chromosome.
2. Alleles are found in pairs and regulate the same trait, such as blood type. Some alleles have a dominant effect, whereas others have a recessive effect.
3. Homozygous is a genetic state in which an individual inherits the same alleles (DNA sequences) for a certain gene from both parents. Here, the alleles are identical. The letters TT or tt stand for homozygous.
4. Heterozygous is a genetic situation in which an individual inherits different alleles (DNA sequences) for the same gene from both parents. In this case, the alleles are not similar. Tt is a heterozygous individual.
5. When two copies of the same or distinct alleles of a gene exhibit the same or different traits, the dominance-recessive connection is used. When an allele is present, the trait of a dominant allele is always visible in the organism. The presence of a dominant allele hides a recessive allele.

Explanation of the incorrect option:

Option B:

A dominant allele expresses itself in all the generation.

Option C:

A dominant allele expresses itself in both homozygous and heterozygous condition.

Option D:

A dominant allele expresses itself in both homozygous and heterozygous condition.

Final answer: A dominant allele expresses itself in both homozygous and heterozygous condition.