Dominant And Recessive Genes

Where one germ cell contains a mutant allele and the other germ cell contains the 'normal' allele the resulting fertilised cell will contain one mutant allele and one normal allele. If the offspring are changed due to the presence of this one mutant allele in the fertilised cell then the mutant gene is dominant.

Where a cell contains one dominant mutant allele and one normal allele this is referred to as the heterzygote and where the cell contains two of the dominant mutant allele this is referred to as the homozygote.

If the mutant allele must be present in both germ cells (ie the fertilised cell contains only the mutant allele and no 'normal' allele) for changes in the offspring to be seen then the mutant gene is recessive.