Hardy Weinberg HELP!

[shscatch08]

So I am in a bio class, and i am so lost on everything! If anyone has any tips for catching up quickly on all of this that would be great!

Here is the problem...

In a class, 27% of the students are PTC tasters (a dominant trait), whereas 63% are non-tasters. (note: the square root of 0.27 = 0.52, the square root of 0.63 = 0.79)

I need to find the frequency of the dominant allele and the recessive allele. I know the formula, but I don't know where to plug things in. HELP!

[mith]

Write out the genotypes, and figure out what the formula means.

[shscatch08]

I have, but i still don't understand.

I know that...

p= frequency of dominant allele
q= frequency of recessive allele
p^2 = % of homozygous dominant individuals
q^2 = % of homozygous recessive individuals
2pq = % of heterozygous individuals

and... p^2 + 2pq + q^2 = 1 and p + q = 1

I just don't understand how to use the formula.

So.. would the frequency by 27 % for the dominant allele? ( That seems to easy, and I don't understand it...)

[mith]

The dominant allele is present in both heterozygotes and homozygotes so no, its not that simple.

[alextemplet]

The formula (p^2, q^2, and 2pq) will tell you the frequency of each genotype. Then figure out which alleles correspond to which genotypes.

[RGoodman]

hi,

I have a little problem with the question u have posted. are you sure those are the right percentage values. because the square of each, eg. the square of 0.27 = 0.52 (rounded up) and the sqaure of 0.63 = 0.79 (rounded) however both these values add up to give 1.31 which in hardyweinberg should be 1. so your percentages must be wrong to start with. if you need any more help give us a shout and i will happily lend a hand.

Bob

P.S. if u want i can take you through step by step of the calculation.

[alextemplet]

No, 0.27^2 is 0.0729, and 0.63^2 is 0.3969. 2*0.27*0.63 is 0.3402.

[RGoodman]

sorry my bad. was late last night when i was doing that and i hit the wrong buttons on my calculator lol yeah the above post is correct. so just to clarift:

0.27*0.27 or 0.27^2 = 0.0729
0.63*0.63 or 0.63^2 = 0.3969

now you find the square of the above values:

square of 0.0729 = 0.27
square of 0.3969 = 0.63

0.027 + 0.63 = 0.9 (close enough to 1) lol

if the is wrong someone say, but from my understanding this give you the p value and q value. (q = recessive, p = dominant)

P.S. Hope this is right, if not ignore everything lol