Black and White Lambs
White wool color is a dominant trait and black wool color is a recessive trait. Credit: Bjorn Forsberg/Oxford Scientific/Getty Images

Genotype - Definition:

Genotype refers to the gene composition of an organism or cell for a given trait. Genotype is inherited through sexual reproduction and differs fromĀ phenotype. Phenotype refers to physical characteristics, such as height and color, that are expressed. An organism's genotype determines its phenotype. When the alleles for a given trait are homozygous, the genotype is identical.

When the genotype is heterozygous, the alleles are different. Heterozygous alleles exhibit different types of genetic dominance relationships. Examples of these relationships include complete dominance, incomplete dominance, and co-dominance.


Genotype is determined by an organism's allele composition. Using wool color in sheep as an example, one allele produces white pigmentation and the other allele produces black pigmentation. The allele for white color is represented as (W) and the allele for black color is represented as (w). In this relationship, the white wool color is dominant and the black wool color is recessive. There are two possible genotypes for a sheep with the white wool phenotype: WW or Ww. A sheep with the (Ww) genotype is a carrier for the black wool color gene. The genotype for a sheep with the black wool phenotype is (ww).