Genotype and its types

The specific combination of genes in an individual is known as genotype. It is of two types i.e. homozygous and heterozygous. In order to understand the concept of genotype, let us consider an example trait i.e. albinism. Like other traits, it is also controlled by one pair of genes. We can represents the two alleles of the pair as ‘A’ and ’a’. There combination i.e. genotypes are possible for these two alleles i.e. AA, Aa, and aa. These genotypes can be grouped into two types. The genotype in which the gene pair contains two identical alleles (AA or aa), is called homozygous genotype. The genotype in which the gene pair contains two different alleles is called heterozygous genotype.

When in the heterozygous condition one allele makes or prevents the expression of the other, it is called the dominant allele. The allele which is not expressed is called recessive.

The dominant alleles are represented by capital letters and recessive alleles by lower case letters. Albinism is a recessive trait i.e. It is produced when both alleles recessive. In humans, allele ‘A’ prod body pigments while allele @a’ does not produce pigments. If genotype is AA or Aa, the individual will produce pigments. On the other hand if genotype is aa, no pigments will be produced and the individual will be albino. In this example, you see that the allele ‘A’ dominates over ‘a’, because in Aa individual pigments are produced and the effect of ‘a’ is suppressed by ‘A’. The expression of this genotype in the form of trait is known as the phenotype.