An allele that exerts its effects whenever it is present is:

• A. Recessive.
• B. Heterozygous.
• C. Dominant.
• D. Homozygous.
• E. Homologous.

Answer: (C)

Verified step by step guidance

1. Understand the concept of an allele: An allele is a variant form of a gene. Each individual inherits two alleles for each gene, one from each parent.
2. Learn the definition of a dominant allele: A dominant allele is one that exerts its effects and determines the phenotype whenever it is present, regardless of whether the other allele is dominant or recessive.
3. Contrast dominant alleles with recessive alleles: A recessive allele only exerts its effects when paired with another recessive allele (homozygous recessive). If paired with a dominant allele, the dominant allele will mask the effects of the recessive allele.
4. Review the term heterozygous: Heterozygous refers to having two different alleles for a gene, one dominant and one recessive. In this case, the dominant allele will determine the phenotype.
5. Understand why 'dominant' is the correct answer: The problem asks for the type of allele that exerts its effects whenever it is present. By definition, this is a dominant allele, as it influences the phenotype regardless of the other allele present.