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# Hardy-Weinberg equation

This equation relates allele frequencies to genotype frequencies for populations in Hardy-Weinberg equilibrium. Created by Sal Khan.

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• why do you need to square the equation? (p + q = 1) •  It is p2+ 2pq+q2 because you are talking about the frequency of alleles and we are diploids i.e. we have 2 alleles for each trait, one allele we receive from our father and another from our mother. Thus,
p2= dominant allele i.e when we have both 'p' from parents
q2= recessive allele i.e when we have bothe 'q' from parents
and 2pq= heterozygote i.e. when we have say'p' from one parent and 'q' from another parent.
Thus in order to understand the equation p+q=1 in terms of diploid organisms we need to square the contents.
• Plus, shouldn't it be equilibrium. The powers balance the alleles...I do understand it IS an equation. Its just nomenclature right? •  The Hardy Weinberg equation describes a hypothetical "ideal" population in perfect equilibrium. It can't truly exist in nature, simply because there's always some force acting on a population. It's used as a reference point.
• Why can't you use the Hardy-Weinberg Principle for a small population? • If you choose your population wisely, and the observed genotype frequencies do not match the expected, what must be the case (according to H-W)? • • In the example given in the video, I am not sure why p^2 represents the probability of an individual being homozygous dominant because it looks like from the example, the two genotypes in question are Bb or bb. so BB would't even be possible would it? if the probability of getting just the B allele is 1/4, then p^2 should equal 1/16 or the probability of a homozygous dominant individual... but again is a BB individual even possible in the example of the two individuals given.

Hope my question was clear! thanks in advance! • The example numerically is not related to the equation as the Hardy Weinberg Equation requires that a population be large and in the previous example, the population is very small, so the requirements for the Hardy Weinberg Principle are not met. Sal is simply using the alleles from the previous example to demonstrate the Hardy Weinberg Equation, but not the numbers. If it helps, just think of BB, Bb, and bb, and ignore everything else. But if the population did met the Hardy Weinberg Equation theoretically, the 3 Genotypes possible would be Bb, BB , and bb.
• what does mean for the equation
given by hardy-wein berg • It is a conceptual idea of population equilibrium that was developed by 2 scientists G.H. Hardy and William Weinberg, who suggested some assumptions for stable, non evolving population in which "allele frequencies do not change and therefore evolution does not occur". theses assumptions are :
1. No mutation
2.No small population
3.No sexual selection
4. No gene flow
5. No natural selection
In order to express Hardy Weinberg principle mathematically , suppose "p" represents the frequency of the dominant allele in gene pool and "q" represents the frequency of recessive allele. p+q=1 since the sum of both frequencies is 100% . In gene pool that include allele p and q the possible genotypes are
.................. Females
.................. (p) (q)
Males (p) 25% (pp) 25%(pq)
..... (q) 25%(qp) 25%(qq)
The total of all genotypes should be equal to 1 so
p^2+2pq+q^2=1
where
p^2=freq. of the HOMOZYGOUS DOMINANT GENOTYPE
2pq=freq. of HETEROZYGOUS GENOTYPE
q^2=freq. of the HOMOZYGOUS RECESSIVE GENOTYPE
p^2+2pq= freq. of the DOMINANT PHENOTYPE
q^2=freq. of the RECESSIVE PHENOTYPE  • 