Can someone PLEASE explain how this makes sense The inputted

Can someone PLEASE explain how this makes sense. The inputted genotype frequencies are NOT THE SAME as the ones calculated for in the second part. Why couldnt he just use F(AA)=p^2 TO BEGIN WITH? Then it would have returned ACCURATE genotype frequencies. PLEASE HELP I AM DESPERATE.

Guppies (Poecilia reticulata) are small, brightly colored fish that are common in freshwater streams in Trinidad. Imagine that the coloration is controlled by two alleles at a given gene. On a sampling trip, a young ecologist collects the following: 200 Brown guppies (AA) 600 Red guppies (Aa) 200 Yellow guppies (aa) Assuming HW equilibrium, calculate the Pallele frequency& the F, genotype frequency of the guppy population. 0.5 0.5 (0.5) f(AA) p 0.25 2 (0.5 0.5) 0.50 0.25

Solution

The frequency of AA individual will be p² =200/1000=0.2

The frequency of Aa individuals will be 2pq= 600/1000=0.6

The frequency of aa individuals will be q² =200/1000=0.2

The frequency of A allele =D +H/2= p² + pq =0.2+0.3 =0.5

The frequency of a allele =R +H/2= p² + pq =0.2+0.3 =0.5

Expected mating frequencies and offspring genotypic frequencies

F2 genotypic frequencies

Mating pattern

Mating frequency

AA

Aa

aa

AA X AA

D^2

D^2

AA X Aa

2DH

DH

DH

AA X aa

2DR

DR

Aa X Aa

H^2

H^2/4

H^2/2

H^2/4

Aa X aa

2HR

HR

HR

aa X aa

R^2

R^2

If we total the columns for each offspring genotype and call the new genotypic frequencies D\', H\', and R\' we get:

D\' = D^2 + DH + H^2/4

H\' = DH + 2DR + H^2/2 + HR

R\' = H ^2/4 + HR + R^2

NEW FREQUENCIES

D\' = D^2 + DH + H^2/4 = (D + H/2)^2 = p^2

H\' = DH + 2DR + H^2/2 + HR = 2(D + H/2)(R + H/2) = 2pq

R\' = H2/4 + HR + R^2 = (R + H/2)^2 = q^2

Mating pattern	Mating frequency	AA	Aa	aa
AA X AA	D^2	D^2
AA X Aa	2DH	DH	DH
AA X aa	2DR		DR
Aa X Aa	H^2	H^2/4	H^2/2	H^2/4
Aa X aa	2HR		HR	HR
aa X aa	R^2			R^2