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Hardy Weinberg question in A level biology please help

I'm a bit confused when to know if x = p^2+2p or weather p is just p^2 (or is it never just p^2 and is only just p or just p^2+p2), god this is going to sound so confusion lol. So in context of a question:
"A population of summer squash plants only produced green and yellow fruit, the percentage of plants producing yellow fruit in the population was 36%, calculate the percentage heterozygous for gene b (yellow)"

So I initially did: p^2= 0.36 and got an answer of 48% heterozygous. This was wrong the answer was 32% as I was meant to do p^2+p = 0.36, so is it never just equal to p^2?

I hope this made sense, sorry if it didn't..
Reply 1
Original post by Student2011584
I'm a bit confused when to know if x = p^2+2p or weather p is just p^2 (or is it never just p^2 and is only just p or just p^2+p2), god this is going to sound so confusion lol. So in context of a question:
"A population of summer squash plants only produced green and yellow fruit, the percentage of plants producing yellow fruit in the population was 36%, calculate the percentage heterozygous for gene b (yellow)"

So I initially did: p^2= 0.36 and got an answer of 48% heterozygous. This was wrong the answer was 32% as I was meant to do p^2+p = 0.36, so is it never just equal to p^2?

I hope this made sense, sorry if it didn't..

i had the same issue and got the exact same answer as you for this question! AQA biology right?? Apparently when they say 'population' that refers to the p^2 or q^2 however since they have asked about the specific gene/allele that refers to p/q not squared. I am confused on this myself not sure if that helps
Reply 2
Original post by Student2011584
I'm a bit confused when to know if x = p^2+2p or weather p is just p^2 (or is it never just p^2 and is only just p or just p^2+p2), god this is going to sound so confusion lol. So in context of a question:
"A population of summer squash plants only produced green and yellow fruit, the percentage of plants producing yellow fruit in the population was 36%, calculate the percentage heterozygous for gene b (yellow)"

So I initially did: p^2= 0.36 and got an answer of 48% heterozygous. This was wrong the answer was 32% as I was meant to do p^2+p = 0.36, so is it never just equal to p^2?

I hope this made sense, sorry if it didn't..

The key to Hardy Weinberg is usually to look at the homozygous recessive phenotype. It might help to ignore p and q and convert the format to B and b, since it is showing you the same thing. So B + b =1, and B^2 + 2Bb + b^2 = 1

In the question, 36 % of the plants were yellow. This occurred if you had either BB or Bb. Whatever is left must be due to the hom rec, in other words bb = 64 %

Convert to decimal: bb = 0.64

Root 0.64 = 0.8. The frequency of b in the population is 0.8

B + b =1, so 1- 0.8 = 0.2.

B = 0.2

To calculate heterozygote, you have 2 x (0.8 x 0.2) = 2 x ( 0.16) = 0.32

Heterozygotes = 32 %

I think you may have initially confused what the genotype results in. If it helps, write out the genotypes and Phenotypes beforehand so you don't lose track:

BB = green
Bb = green
bb = yellow (36% or 0.36)

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