Question

An allele is described as ‘dominant’ if it expresses itself when it occurs in
A. Heterozygous condition
B. Homozygous condition
C. Both heterozygous condition and homozygous conditions
D. Hemizygous condition

Answer 1

Hint: An allele is one of the forms of a gene that may occur alternatively at a given site on a chromosome. The dominant occurs when a trait is exhibited by two copies of the same or different alleles of a gene. Use this info to answer the question.

Complete answer:
An Allele is also called an allelomorph. Alleles occur in pairs and control the same characteristic such as blood type. Some alleles are dominant and some others are recessive.
Zygosity is the degree of similarity of the alleles in an organism.
Homozygous is a genetic condition where the same alleles (DNA sequence) for a particular gene from both the parents are inherited by an individual. The alleles are identical here. TT or tt are homozygous.
Heterozygous is a genetic condition where different alleles (DNA sequence) for a particular gene from both the parents are inherited by an individual. The alleles are not identical here. Tt or tT are heterozygous.
The dominance-recessive relationship is applied when a trait is exhibited by two copies of the same or different alleles of a gene. A dominant allele’s trait always shows up in the organism when an allele is present. A recessive allele is masked by the presence of a dominant one.
Therefore, a dominant can be either TT or Tt. Hence in both homozygous and heterozygous conditions, a dominant allele can occur.

So, the correct answer is “Option C”.

Note:
Do not confuse allele with a gene. Alleles are different forms of the same gene. A gene can have at least two alleles. Gene is an organism’s genotype whereas an allele is an organism’s phenotype. Gene examples are hair color, eye color whereas allele examples are blue eyes, black hair, dark skin.