# Biology A-level help

Hi, can anyone plz help me with this biology question?

In a zoo, there are 325 guinea pigs and 52 of them have long fur which are recessive. Using the Hardy-weinberg principle, predict how many of the guinea pigs will be heterozygous for the fur length allele.

P.S- the answer is 156, I just want to know how the answer was got.
Original post by Laychips
Hi, can anyone plz help me with this biology question?

In a zoo, there are 325 guinea pigs and 52 of them have long fur which are recessive. Using the Hardy-weinberg principle, predict how many of the guinea pigs will be heterozygous for the fur length allele.

P.S- the answer is 156, I just want to know how the answer was got.

p^2 + 2pq + q^2 = 1
The "1" corresponds to the whole population 325 guinea pigs. For the equation to work, you essentially need to turn the "325" into "1" do this by dividing by 325. [ratio and proportion etc.]
Now for the q^2 bit, or 52 guinea pigs. To get the proportion, just divide by 325. This is q^2.

p + q = 1
You can calculate q by finding the square root of q^2 from above. Then you can work out p.

Heterozygous = 2pq
So use your values of p and q to calculate the proportion of guinea pigs that are heterozygous.
Then multiply this by the actual population size (325) and bingo you get 156

Apologies if this is a bit of a long-winded/confusing way to go about it!
When doing a Hardy-Weinberg equation, I always start by calculating the q^2 (recessive value), which would be 52/325 in this instance.
You also need to use the p+q=1 equation, so then square root your q^2 value to get the value of q on its own, which can then be taken away from 1 to get the value of p.
From there you have the values for both p and q so can use them in the calculation of 2pq to find the heterozygous phenotype.
Then all you have to do to find the number of individuals in the population with that phenotype is to multiply the 2pq value by the total population (325) which equals 156.

Hope that makes sense? (:
Original post by butterfliesss
When doing a Hardy-Weinberg equation, I always start by calculating the q^2 (recessive value), which would be 52/325 in this instance.
You also need to use the p+q=1 equation, so then square root your q^2 value to get the value of q on its own, which can then be taken away from 1 to get the value of p.
From there you have the values for both p and q so can use them in the calculation of 2pq to find the heterozygous phenotype.
Then all you have to do to find the number of individuals in the population with that phenotype is to multiply the 2pq value by the total population (325) which equals 156.

Hope that makes sense? (:

Thank u!!