Bt Genetics Presentation

7/30/2019 Bt Genetics Presentation

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BT:414-Genetics

Hardy WeinbergsEquilibrium

Presented by:

Amrita Kumari

Aniket Girish ParabKabita Sharma

Elice

Iooni wanhi Law

2nd Sem.,M.Sc,MBBT,T.U .


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Hardy-Weinberg Principle

Godfrey H. Hardy

Wilhelm Weinberg

It states that in a large randomly breeding population,

allelic frequencies will remain the same from generation

to generation assuming that there is no mutation, gene

migration, selection or genetic drift.

This principle is important because it gives biologists astandard from which to measure changes in allele

frequency in a population.


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Contd.

The HardyWeinberg principle (also known as the Hardy-Weinbergequilibrium) states that both allele and genotype frequencies in a

population remain constantthat is, they are in equilibriumfrom

generation to generation. This assumes that, within a given

population:

1. Mating is random

2. No mutations are arising

3. No gene flow

4. No natural selection

5. Population size is infinitely large


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The Hardy-Weinberg principle can be

illustrated mathematically with the equation:

p+2pq+q = 1 Where p and q represent the frequencies of alleles.

Example.


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Determination of the degree of

variation of the population from

HWE When a population meets all of the of the Hardy-Weinberg

conditions, it is said to be in Hardy-Weinberg equilibrium(HWE).

However, human populations only seldom meet all of theconditions of HWE exactly, and thus their allele frequencieswill change from one generation to the next and thepopulation will evolve.

How far a population deviates from HWE can be measuredusing the goodness of fit or chi-squared test (2).

Example.


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1.Random Mating


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2.Mutation

Both mutations and recombination can alter the allelic frequencies

from generation to generation and, at least in theory in small

populations, can affect HWE.

Recombination Mutation


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Case study on mutation


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3.Migration and Gene Flow

Migration

Allele frequencies will change if migration occurs into or away from the

population. The effect of migration on HWE is dependent on the

difference in allele frequencies between the donor and recipient

populations.

Gene Flow

Gene flow is another way to introduce genetic variability to a

population. Similar to migration, it occurs when members of one genepool mate with members of another gene pool, which can lead to an

alteration of the allele frequencies


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4.Genetic Drift

Genetic Drift

Allele frequencies in small populations do not generally reflect

those of larger populations since too small of a set of

individuals cannot represent all of the alleles for the entire

population.- Occurs when the population size is limited and therefore by

chance, certain alleles increase or decrease in frequency.

- This can result in a shift away from Hardy-Weinberg

equilibrium (HWE).- Unlike natural selection, genetic drift is random and rarely

produces adaptations to the environment.


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5.Natural Selection

Darwin termed the phenomenon of changes that

allowed organism to adapt to their environment within

populations, natural selection, and proposed the idea of

survival of the fittest.

Over a long period of time, this change in the

characteristics of a population can lead to the production

of a new species

Wh h h h


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What happens when the

population remains in HWE for

longer time?

Inbreeding depression

Linkage Equilibrium is disturbed(Linkage disequilibrium)


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REFERENCES

Hardy, G.H. 1908. 'Mendelian proportions in a mixed population.'

Science, vol. 28, 49-50.

Merten, Thomas R. February 1992. 'Introducing students to population

genetics and the Hardy-Weinberg Principle.' The American BiologyTeacher, vol 54, no. 2. pp. 103-107.

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