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population genetics

The work of a biologist to describe the genetic composition of the population by specifying the frequency of alternative genotypes


genotypic frequency

The fraction of a population that carries a specific genotype


gene frequency

The frequency of an allele in the pool of all available gametes (a population)


Hardy-Weinberg equilibrium

When no other forces (such as natural selection) are operating, genotypic frequencies (distribution of a specific allele in a population) reach stable proportions in just one generation. If this F1 generation mates at random, distribution of genotypes in F2 will remain exactly the same as the distribution of genotypes in F1


Hardy-Weinberg proportion equations for a genetic locus with two alleles

freq(aa) = q^2
freq(Aa) = 2pq
freq(AA) = p^2

q = freq of allele a
p = freq of allele A


Natural Selection

If different genotypes are associated with different phenotypes and those phenotypes differ in their ability to reproduce, then the alleles that led to the development of the favoured phenotype will increase in frequency


As long as all genotypes are equally likely to survive what will happen to a population?

It will remain at Hardy-Weinberg proportions, a stable state of equilibrium


Three principles of natural selection

1) can not produce change unless there is variation in the population (ex not heterozygous)
2) selection does not operate directly on genes, it changes the frequency of different phenotypes
3) the strength and direction of selection depend on environment


environmental variation

Phenotypic expression of all characters, whether affected by one or many loci, depends on the environment the organism is in (ex. nourishment during development)


modern synthesis

The reconciliation of Mendelian genetics and Darwinism, resulting in a body of theory that solves the problem of explaining how variation is maintained through generations



Variation added to a population through the introduction of new alleles due to damage to DNA caused by certain types of ionising radiation or chemicals