A chromosome is special DNA structure that comes from its packaged organization so it can all fit in a small nucleus within eukaryotic cells. In humans, DNA aggregates to form 24 pairs of chromosomes whereas snow leopards only have 19 pairs. In most mammals gender is determined thanks to the presence of a specific pair of chromosome: X and Y. Males have a copy of each chromosome whereas females have two copy of the X chromosome. By being able to identify DNA sequences that are to be found only on one of the sexual chromosome, the gender of the snow leopard, from which the analyzed DNA comes from, can be determined.