Which term describes a genotype that contains two different alleles at a given locus?

• A. Homozygous
• B. Heterozygous
• C. Nullizygous
• D. Hemizygous

Answer: (B)

Verified step by step guidance

1. Understand the definition of genotype: it refers to the genetic makeup of an organism at a specific locus, which can include one or more alleles.
2. Recall that alleles are different versions of a gene that can exist at the same locus on homologous chromosomes.
3. Identify the term 'homozygous' as describing a genotype where both alleles at a locus are the same (e.g., AA or aa).
4. Recognize that 'heterozygous' describes a genotype where the two alleles at a locus are different (e.g., Aa).
5. Note that 'nullizygous' and 'hemizygous' refer to other specific genetic conditions and do not describe having two different alleles at a locus.