Population Genetics is concerned with the frequency of alleles within the population and changes to that frequency over time. The ability to taste phenylthiourea is useful and an important tool in the study of human diversity. It is an important character in population genetics in which variation depends on a pair of allelic gene. Phenylthiocarbamide as known PTC or phenylthiourea is a chemical compound that is made up of elements: carbon, hydrogen, nitrogen and sulphur. Colour blindness is not exactly 'colour blindness'. There are many people who still think colour blind people can't actually see any colours. More than 99% of all colour blind people can see colours. A better wording would be colour vision deficiency, which describes this visual disorder much more precisely. Colour blindness is the decreased ability to perceive differences between some of the colours that others can distinguish. It is most often of genetic nature, but may also occur because of some eye, nerve, or brain damage, or exposure to certain chemicals.