Measuring Genetic Biodiversity

Genetic diversity is the variety of alleles within a species or population. It can be measured in several ways.1. Heterozygosity index. Edexcel uses the heterozygosity index, H:H = number of heterozygotes / number of individuals in the populationA heterozygote has two different alleles of a gene. The more alleles a population has, and the more evenly they are spread, the more individuals will be heterozygous. So a higher H means greater genetic diversity.Worked example. In a population of 250 deer, 85 are heterozygous for a particular gene.H = 85 / 250 = 0.34H is usually worked out for several genes and an average taken, because one gene may not represent the whole genome.2. Counting alleles and polymorphism. Biologists can record the number of different alleles of a gene in a population, and the proportion of genes that are polymorphic (have more than one allele).3. Molecular methods. DNA sequencing, or comparing DNA fragments by gel electrophoresis, shows directly how many differences there are in the base sequences of individuals.Genetic diversity matters because a population with many alleles is more likely to contain individuals that can survive a new disease or change in the environment. Small or isolated populations, and populations that have passed through a bottleneck (a sharp fall in numbers), have low H. For example, the cheetah has very low genetic diversity, which makes it vulnerable to disease. Zoos and seed banks use measures of genetic diversity to plan breeding and collection.