What does genotype refer to?

Genotype refers to an organism's genetic makeup and the specific combination of alleles it possesses. It defines the hereditary information encoded in the organism's DNA and determines the potential traits that can be expressed. The genotype encompasses both the alleles that are dominant, recessive, or co-dominant, and it directly influences the phenotype, which represents the observable traits that result from this genetic information.

The other options present concepts that do not accurately define genotype. Observable traits are related to phenotype, while a complete set of chromosomes pertains more to the organism's chromosomal composition. The influence of the environment on gene expression relates to epigenetics, which examines how external factors can affect how genes are expressed, but this is separate from the definition of genotype itself.