Exercise+6

__**WIKISPACE EXERCISE 6.

Group members: Mediha Aziz, Pooja Limbani, Joe London and Sukhman Athwal.

Hardy-Weinberg Principle.**__

In population genetics, the Hardy-Weinberg principle, defined by Godfrey Hardy and Wilhelm Weinberg, presents the relationship between the genotype of a population and the frequency of alleles. Also referred to as Hardy–Weinberg equilibrium, the concept of equilibrium relates to the constancy of the occurrence of a genotype, e.g. a genotype associated with a disease, within a population. The occurrence of a genotype associated with cystic fibrosis will remain relatively constant unless mutations occur or breeding becomes non-random. This constancy is due to the equilibrium between the allele frequency and the genotype occurrence, a genetic equilibrium.

Genetic equilibrium is always true if five specific conditions are met:


 * Population size must be large.
 * There should not be gene flow (migration) in the population.
 * Environmental factors should not be causing natural selection to occur.
 * Mutations can not be occurring in the population.
 * Random mating must occur. (Perhaps the most important condition, each organism has an equal opportunity of mating with another organism within the same population).

Heterozygosity is extremely important, as a population needs genetic diversity to survive. Hardy Weinberg can be used to test heterozygosity and the diversity of a population when applying the equation, the answer is a measure of the chance of an individual being born with a heterozygous genotype.


 * E (p2) = V (p) + (E(p))2**

The Hardy-Weinberg principle can also be used to determine the effects of population bottle necks and the founder effect. A population bottleneck is an evolutionary event that occurs when a population is reduced to at least half. This can either be due to them being killed off or being prevented from reproducing. The founder effect is very similar to this but this occurs when a smaller group becomes reproductively segregated from the main population. An example of this is FIP (feline infectious peritonitis) in cheetahs. It is a disease that is lethal in cats caused by a coroner virus. When it came into the cheetahs population, half of the population died out. Where as in other cat populations, most were resistant to it. This illustrates that this cheetahs population of bottlenecks lead to the founder effect and that there really was not enough genetic diversity in the population.

The Hardy-Weinberg principle can be used to analyse allele frequencies from genotype frequencies. For example cystic fibrosis, a genetic disorder, resulting from a mutation in the CFTR gene (cystic fibrosis transmembrane conductance regulator), causes damaging effects on mainly the lungs and the digestive system.

Cystic fibrosis, occurs in 1 in every 1,700 USA Caucasian new-borns, being a recessive genetic disorder, this means that only the homozygous for the disorder within the population can be analysed and detected; heterozygotes are seemingly invisible to the analysis pertaining to the Hardy-Weinberg principle.