Expert: Dana Krempels, Ph.D. - 7/7/2007

Question
Hello,

I am currently taking a biology course correspondence, and have found difficulty with this particular question.

A population has two alleles, B and b. The allele frequency of B is 0.73. What is the heterozygotes frequency, if the population is in H-W equilibrium?

I noticed your writing above saying you wont help people cheat, but what if we genuinely need some advice on how to answer a question? Thanks for you help.

I have tried this question, and either I am incorrect, or the previous textbook examples are.

Rob

Answer
Dear Rob,

If you're studying the allele frequencies of a gene with two alleles, then the frequency of the dominant allele (B) is represented as "p" and the frequency of the recessive allele (b) is represented as "q".  Together, the frequency of both alleles must always equal 1.0 (100% of the alleles of that gene in the population).

So if you know the frequency of B is 0.73 (73%), then that means the frequency of b must be 0.27 (27%).  Now that you have both p and q, you can solve for all the variables in the Hardy-Weinberg equation.

Remember that:

p squared = the proportion of BB individuals in the population

q squared = the proportion of bb individuals

2pq = the proportion of heterozygotes (Bb)

Just plug in the two numbers in the proper places (0.73 for p and 0.27 for q), and you'll have your answer!  :)

Hope that helps.  For some examples of how to do Hardy-Weinberg calculations, please feel free to check out my lecture notes here:

www.bio.miami.edu/dana/250/25007_15.html

Start where it says "Measuring Allele Frequencies" if you want to go straight to HW equilibrium.  But the whole lecture might help you.

Good luck with your course!

Dana