Question

An organism with two identical alleles is

• A. dominant
• B. hybrid
• C. heterozygous
• D. homozygous.

Answer 1

The Correct Option is D

To determine what is meant by an organism with two identical alleles, we must understand some basic genetic terminology.

• Alleles: These are different versions of the same gene. Each organism inherits two alleles for each gene, one from each parent.
• Homozygous: This term is used when an organism has two identical alleles for a specific trait. For example, if both alleles are for blue eye color, the organism is homozygous for that trait.
• Heterozygous: This is the opposite of homozygous, where the alleles for a trait are different (one might be for blue eyes, the other for brown).
• Dominant and Recessive: These terms refer to the expression of traits. A dominant allele will mask the expression of a recessive allele in a heterozygous organism.
• Hybrid: In genetics, this is often synonymous with heterozygous, indicating mixed alleles for a trait.

Given these definitions, an organism with two identical alleles is termed homozygous. This is because "homo" means "same," indicating that the alleles are the same — whether they are dominant or recessive is irrelevant to this definition.

• The option dominant refers to an allele that masks the expression of another but does not specifically indicate identical alleles.
• Hybrid implies a mix of alleles, which would be the opposite (heterozygous).
• Heterozygous specifically means two different alleles, which contrasts with two identical ones.

Thus, the correct answer is homozygous.