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Genetic equilibrium means
Gene pool remains constant
Phenotypes remains constant
Migration of a species into new area
Immigration of species
Solution
Gene pool remain constant.
Hardy-Weinberg Principle
It was proposed by GH Hardy an English mathematician and W Weinberg a German physician independently in $1908$
$(i)$ It describes a theoretical situation in which a population is undergoing no evolutionary change. This is called genetic or Hardy-Weinberg equilibrium
$(ii)$ It can be expressed as $p^{2}+2 p q+q^{2}=1$ or $|p+q|^{2}=1$
$(iii)$ Evolution occurs when the genetic equilibrium is up set (evolution is a departure from Hardy-Weinberg equilibrium principle)
The sum of total of Allelic frequency $\langle p+q|$ is $=1$
$p^{2}+2 p q+q^{2} \text { or }|p+q|^{2}$
Where, $p^{2}=\%$ homozygous dominant individuals
$p=i$ frequency of dominant allele
$q^{2}=\%$ homozygous recessive individuals
$q=i$ frequency of recessive allele
$2 p q=\%$ heterozygous individuals
Realize that $|p+q|^{2}=1$ (three are only $2$ alleles)
$p^{2}+2 p q+q^{2}=1$ (these are the only genotypes)
Example An investigator has determined by the inspection that $16\, \%$ of a human population has a recessive trait. Using this information, we can calculate all the genotypes and allele frequencies for the population, provided the conditions for Hardy-Weinberg equilibrium are met
Given $q^{2}=16 \,\%=0.16$ are homozygous recessive individuals
Therefore,
$q=\sqrt{0.16}=0.4=i$ frequency of recessive allele
$p=1.0-0.4=0.6=i$ frequency of dominant allele
$p^{2}=0.6 \times 0.6=0.36$ or $36 \%$ are homozygous dominant individuals
$2 p q=2 \times 0.6 \times 0.4=0.48=48 \%$ are heterozygous individuals
$i\, 1.00-0.52$
$i \,0.48$
Thus, $84 \%$ ( $36+48$ ) have the dominant phenotype