What term describes the genetic makeup of an individual, i.e., the combination of alleles?

• A. Phenotype
• B. Allele
• C. Gene
• D. Genotype

Answer: (D)

Genotype is the genetic makeup of an individual—the specific combination of alleles at the gene loci being considered. It represents the actual genetic constitution, such as homozygous (two identical alleles) or heterozygous (two different alleles) at each locus. Phenotype, by contrast, is what you can observe—the visible traits that result from the genotype interacting with the environment. An allele is a variant form of a gene, and a gene is the basic unit located at a particular locus that can have different forms. For example, at a coat-color locus, the genotype might be two copies of a dominant allele, two copies of a recessive allele, or one of each, and the phenotype reflects which alleles are present and how they express. The term that describes the combination of alleles an individual carries is genotype.