Lyonisation is a process in which one of the two copies of X chromosomes in female body becomes inactivated. This prevents from making two copies of the product of X chromosomal genes as those of the males which has only single copy of X chromosome called dosage compensation. The X chromosome is silenced and made transcriptionally inactive called heterochromatic body. This process is proposed by Mary Lyon and Liane Russell.

The genetic material that is DNA shows 99 % similarity except some regions has different DNA sequence that is responsible for making difference in various species. VNTRs or Variable Number of Tandem Repeats are the short nucleotide sequences that are present in every individual showing variations in lengths (tandem repeats) and are useful as genetic markers.