Apart from the Homozygous and Heterozygous Allele, there is another rare in occurrence “Hemizygous” Allele found in nature. In the phenomenon of hemizygosity, the progeny receives only one copy of a pair of Alleles from the parental generation. Thus, sometimes one Allele is said to be missing (total Chromosome number is less than normal), however, there are special hemizygous cases with normal Chromosome numbers. Hemizygosity can occur when there is depletion of one of the Chromosomes or during heterogametic sex. Examples of heterogametic sex include males in the human species. They are said to be hemizygous for the X- Chromosome, as they receive only one copy of it from their parental generation.