Four related EGF receptors participate in signaling by the many members of EGF family :

In the mouse - Erb-B1, 2, 3, and 4

In humans - HER 1, 2, 3, and 4

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Genetic bottleneck

Genetic drift arises is through a genetic bottleneck, which develops when a population undergoes a drastic reduction in size

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THE MAGNITUDE OF GENETIC DRIFT

n  = population size

pq=allelic frequency

sp2=variance in allelic frequency among the populations

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Loss of their original diversity per generation

=1/2n

Gain of their original diversity per generation

=1/2n 

Gain or Loss of their original diversity per generation

=1/4n

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Probability of being heterozygote in given population

H = 1 - 1/2N

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Effective population size(Ne)

Effective number of breeding adults in a population.

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Some factor determine Ne

1.Sex ratio.

2.Variation between individual in reproduction success.

3.Fluctuation in population size.

4.The age structure of the population.

5.Mating is random.