HELP on Hardy Weinberg Problem

[iluvcats]

HELP on Hardy Weinberg Problem!

Homework Statement

the allel for unattached earlobes is dominant over the allele for attached earlboes. in a population of 500 individuals 25% show the recessive pheontype. how many individuals woul you expect to be homozygous dominant and heterozygous for this trait?

Homework Equations

p^2+q^2=1.0
p^2+2pq+q^2=1.0

The Attempt at a Solution

q^2=.25
p^2+.25=1.0
p^2=.75
.75 x 500

p^2 =375 people are homozygous dominant


square root of .75 = .87
square root of .25 =.5
2(.87)(.5)
.87
.87 X 500 =435 people are heterozygous

this on one of my many attempts with this problem. i REALLY need some help with it. someone to walk me step by step through it. i know the equation, i have spent plenty of time working on it and i have more of the same problems so if i don't understand one of them than i can't do any. i have looked through all my textbooks and am unable to understand it. so if you could please help me out and help me step by step with so i can understand how to apply the formula to the problem i would really appreciate it. thank you

 

[jim mcnamara]

step 1: q^2 = .25 this is correct.

step 2: You need to know what q is. What is the square root of .25? Answer .50

step 3: You need to know p. The total is always 1.0. So p = 1.0 -q
which is p = 1.0 -.50
which leaves p = .50

step 4:We have p=.5 and q=.5
What percent are homozygous dominant (based on frequency of p)
p times p (from your equation above p^2 + 2pq + q^2=1.0) is the percent of
homozygous dominant - p^2 = .25
How many in the population: .25 x 500 = 125 dominant homozygous

step 5: We now need to know how many heterozygous. Since we know the percent of
homozygous recessive - it was given to us - .25 x 500 == 125 homozygous
recessive.
step 6: We have 500 total. We know 125 are homoz recessive another 125 are homoz
dominant. We used up 250. We have 500. So we are left with 250
heterozygous

So now you have template to work these problems.

 

[iluvcats]

thank you VERY much for helping me. i understand it now. thank you. :)