Module 4: Measuring Genetic Biodiversity
These free OCR A Level Biology Measuring Genetic Biodiversity revision notes have been written for specification points 4.2.1(e) and 6.1.2(f).
Assessing Genetic Biodiversity
Measuring genetic diversity allows scientists to monitor population health, detect signs of inbreeding or bottlenecks, and guide conservation or breeding decisions.
Examples include:
- Endangered wild species, such as cheetahs or Ethiopian wolves, which may have experienced genetic bottlenecks.
- Captive breeding programmes in zoos, where maintaining variation is vital to avoid inbreeding.
- Rare domestic breeds and pedigree animals, where selective breeding can reduce genetic diversity.
Measuring Genetic Biodiversity
Genetic diversity calculations are especially useful when assessing populations at risk of low genetic variation.
The proportion of genotypes for an allele in a population can be calculated using the Hardy–Weinberg equation.
There are three common ways to measure or estimate genetic biodiversity:
- Hardy–Weinberg equation*: Predicts expected genotype frequencies in a population, assuming no migration, mutation, random mating, a large population size, and no selection pressure.
- Polymorphic gene loci: Estimates the proportion of gene loci in a population that have more than one allele.
- Heterozygous gene loci: Estimates the proportion of gene loci in an individual that are heterozygous.
*A2 content only, but presented here for relevance.
The Hardy–Weinberg Equation
The Hardy–Weinberg principle predicts expected genotype frequencies within a non-evolving population (allele frequencies do not change across generations).
p² + 2pq + q² = 1
Where:
- p = frequency of the dominant allele (A)
- q = frequency of the recessive allele (a)
- p² = homozygous dominant (AA)
- 2pq = heterozygous (Aa)
- q² = homozygous recessive (aa)
Because p + q = 1, knowing one allele, or genotype, frequency allows the rest to be calculated.
Determine The Percentage Polymorphic Gene Loci
You can calculate the proportion of gene loci in a population that are polymorphic.
Proportion of polymorphic loci = (Number of polymorphic loci) ÷ (Total number of loci)
To express this as a percentage:
Genetic diversity (%) = (Polymorphic loci ÷ Total loci) × 100
Determine The Number of Heterozygous Gene Loci in an Individual
An individual’s genetic diversity can be estimated by calculating the proportion of loci for which it is heterozygous:
Heterozygosity (%) = (Number of heterozygous loci ÷ Total loci in genome) × 100