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Genetics : Population Genetics
Transcript of Genetics : Population Genetics
last two hundred years has been studied in detail
Gene pool :The stock of different genes in an interbreeding population
Evolution is defined as "a change in the frequency of an allele within a gene pool"
Three of Darwin's 10 children died in childhood,
while another three never had any children of their own, despite being married for years.
# Offsprings increase the frequency of variation increases
Types of selection
Hardy weinbergs equation
Adaptation: fitness, fecundity and viability
Annie, Darwin's adored eldest daughter, succumbed to TB at the age of 10.
why, after many generations, a population didn’t
come to be composed solely of individuals with the dominant
The Hardy–Weinberg principle
No mutation takes place.
No genes are transferred to or from other sources
no immigration or emigration takes place
Random mating is occurring.
The population size is very large.
No selection occurs.
The Hardy–Weinberg equation with two alleles:
A binomial expansion
In algebraic terms, the Hardy–Weinberg principle is written as
sum of the
three genotype frequencies must also equal 1
P + 2 pq + q
p + q = 1
In industrialized areas throughout Eurasia and North America,
dozens of other species of moths have evolved in the same way
as the peppered moth
P + q = 1
what is normal ?
Human interacted selection pressure
Bottle neck effect
Natural selection :
Natural selection is the gradual natural process by which biological traits become either more or less common in a population as a function of the effect of inherited traits on the differential reproductive success of organisms interacting with their environment. It is a key mechanism of evolution.
1. Descent with modification
2. Common Decent
Natural selection was emphasized by Darwin the Naturalist
Skin less chicken
How do we define normal ?
What happens if the genetic variation decreases ?
Consider a population of 100 cats in which 84 are
black and 16 are white. The frequencies of the two phenotypes
would be 0.84 (or 84%) black and 0.16 (or 16%) white. Based
on these phenotypic frequencies, can we deduce the underlying
frequency of genotypes?
p = frequency of the dominant allele in the population
q = frequency of the recessive allele in the population
p2 = percentage of homozygous dominant individuals
q2 = percentage of homozygous recessive individuals
2pq = percentage of heterozygous individuals
You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following:
The frequency of the "aa" genotype.
The frequency of the "a" allele.
The frequency of the "A" allele.
The frequencies of the genotypes "AA" and "Aa."
The frequencies of the two possible phenotypes if "A" is completely dominant over "a."
Hardy-Weinberg equilibrium cannot exist in real life
thus allowing a simplified method of determining that evolution is occurring
Kind of the 5th outcome .....
The conclusion :
the original proportions of the genotypes in a population
will remain constant from generation to generation, as long as
the following assumptions are met:
“devil facial tumor decease”
Q. Define Selection
Factors contributing to speciation
State your own theory of speciation supporting with proper evidence .
( P )
1. Gene Pool
But , Hybrids cannot mate and
produce off springs