Genes can be described as basic hereditary units. The genes are made up of DNA.
A gene carries two alleles for a particular trait. These alleles are present at the same loci in the homologous chromosomes. If the two alleles are similar then they are termed as homozygous e.g AA, BB. If the alleles for a trait are different then they are termed as heterozygous e.g Aa and Bb.
