15-06-2013, 04:55 PM
POPULATION GENETICS
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Population genetics is the study of allelic variation among individuals , the transmission of allelic variation from parents to offspring generation after generation & changes that occur in genetic make up of a population.
Gene Pool
The aggregate of all the genes & their alleles present in an interbreeding population is called gene population.
In a gene pool there is shuffling & reshuffling of alleles of different genes.
Gene Or Allelic Frequency
The proportion of an allele in relation to the total of all the alleles present at a particular locus in a breeding or menedelion population is called gene frequency.
Gene frequency can change due to gene flow, gene exchange, mutation & inbreeding.
Each gene in a genome exists in different allelic state.
A diploid individual is either a homozygous or heterozygous within a population.
We can calculate the frequencies of different types of homozygous or heterozygous of a gene.
Hardy-Waeinberg conditions
Population is large
Population is closed i.e. no immigration or emigration
No seasonal fluctuations in the size of mating population
Mating must be random
Equal proportion of male & female
No mutation rate of forward & reverse mutation is equal
Chromosome aberration absent
Meiosis is normal
No natural selection
Random Genetic Drift
Random fluctuation in gene frequencies of a population due to chance or sampling error in a small isolated population is called –random genetic Drift or genetic drift or random drift or Wright effect.
In small population the chances of inbreeding increases.
Inbreeding decreases the chance of heterozygocity & increase chance of homozygosity.
Ultimately one allele may be lost from the population while the other allele become fixed.(frequency =1)
Allele fixation is the phenomenon by which an allele come to have a gene frequency of one .
The fixed allele may be dominant p = 1 or recessive q = 1.