# Is this a simple Hardy-Weinberg problem?

Phenylketonuria is a severe developmental disability due to a rare autosomal recessive allele. Approximately 1 in every 10,000 newborns suffer from this disease. Calculate the frequency of the allele causing this disease and the frequency of heterozygous "carrier" individuals.

What I've come up with is that this is a Hardy-Weinberg problem. Is this true? My answers: frequency of allele causing disease = 0.01 frequency of heterozygous "carrier" individuals = 0.0198

• Yeah you are right but what are your reasons for thinking that this is a Hardy weinberg problem ? Oct 21, 2015 at 12:50
• I honestly have no idea. I just tried the numbers that semi made sense and it seemed to answer the questions at hand. Is there a method that reveals why this is exactly a Hardy-Weinberg problem? Oct 26, 2015 at 4:08
• See my ans. And yeah I also think this is the "bestest" site ever !! Oct 26, 2015 at 12:52

Too long for comment :

If you want to solve the question by Hardy Weinberg, there are certain assumptions involved :-

1.There is random mating. People do not choose their mates on the basis of whether they carry PKU gene or not & mating among close relatives is not there.

2.No new PKU mutations happen.

3.There is no difference in the reproductive capacity of people with or without PKU gene.

If your study population fulfills these criterias, you can apply Hardy-Weinberg to calculate frequencies of various genotypes.

Because this question is homework ,such assumptions are not mentioned. And, at undergrad level,there is no other concept by which you can solve this question except HWE.

PS: Try to think what would happen if these assumptions are not fulfilled.

PSS: Even if you are solving a small homework question, do think about the logic behind every step. Though it may seem like a lot of work initially , it has enormous potential to teach you subtle concepts !

• The fact that PKU is a "severe developmental disease" makes me think that assumption #3 is violated. It could be that the students are meant to solve the problem with the HW equation anyway, though
– C_Z_
Oct 26, 2015 at 18:35
• @cactuswoman If PKU is diagnosed early and diet restrictions are followed, it is possible to live "normally". Oct 27, 2015 at 1:00

Yes, your answers are correct. Of course, your calculations forced you to make the standard Hardy-Weinberg assumptions such as random mating. Good job!

• This should be a comment. Oct 26, 2015 at 13:40
• Well... The OP is asking did I get it right? The answer is either no, because... or yes. Oct 26, 2015 at 15:11