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Population genetics

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james rawlings

on 13 October 2011

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Transcript of Population genetics

Population genetics A group of individuals carries a larger number of different alleles than an individual.

This gives rise to a pool of genetic diversity that can be measured using the HARDY-WEINBURG EQUATION.

Factors that affect the amount of genetic variation within a population are:
Genetic drift.
Mutation Birth of population genetics Both Darwin and Mendel developed the concept of genes and alleles; they began to understand the genetic basis of inherited variation. As they studied evolution they realised that populations rather than individuals are the functional units in this process. Scientists realised that they needed to consider the frequency of alleles in the population and not just offspring from individual matings.

Early in the twentieth century Hardy and Weinberg, developed the basic principles of population genetics.

In population genetics focus on the genetic structure of population. They measure changes in alleles and in genotype frequency from generation to generation. Measurement of allele and genotype frequencies. We observe the phenotype of the individuals. To measure the frequency of the allele, we need to know:
 The mechanism of inheritance of a particular trait.
 How many different alleles of the gene for that trait are in the population. For traits shown in codominance the frequency of the heterozygous phenotype is the same for the heterozygous genotype. In the MN blood group the gene L has two alleles Lm and Ln .

Each allele controls the production of a specific antigen on the surface of red blood cells.

An individual may be (pheno) type M (genotype: LmLm or MM), type N(LnLn or NN) or type MN(LmLn or MN).

Because these alleles are codominant, we can determine the frequency of the alleles in a population. However if one allele is recessive, the heterozygotes show the same phenotype as the homozygous dominant individual. This means that the frequency of the alleles can’t be directly determined. It makes the following assumptions:
 The population is very large.
The mating with in the population is random.
There is no selective advantage for any genotype.
There is no mutation, migration or genetic drift. The Hardy-Weinberg principle They developed a mathematical model to calculate the allele frequencies, in populations, for traits with dominant and recessive alleles. It’s one of the most fundamental concepts in population genetics. Example see sheet
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