What does genotype refer to in genetics?

• A. An organism's observable characteristics, such as height and eye color.
• B. An organism's genetic makeup, or allele combinations.
• C. The number of chromosomes in a gamete.
• D. The environmental conditions that influence development.

Answer: (B)

Genotype refers to an organism's genetic makeup—the specific alleles at the genes it carries. It’s the actual combination of alleles inherited from the parents (for a given gene, examples are AA, Aa, or aa), which sets the potential for traits to be expressed. This is distinct from the trait you can see, the phenotype, because environment and other factors can influence how those genes are manifested in an organism. It’s also not about how many chromosomes are in a gamete or about environmental conditions themselves. For example, the genotype determines which alleles are present for a trait like eye color, even though the final color we observe (the phenotype) depends on how those alleles are expressed.