Hardy Weinberg

[dentalduck15]

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I have a general question.

If given a hardy weinberg problem, how do you know if to plug it into the p^2+2pq+q^2 equation or the p+q=1 equation to get the answer. Like, if the problem said that the homo recess allele is 9% how do you know where to plug it in.

And, an irrelevant question:
If you are given the diploid number of a species, like 2n=46, how do ou determine the chromosomes or chromatids at a specific state in the division process.

thanks. I know these are easy but Im messing them up half the time.

 

[sshar43]

Hey there!

For Hardy-Weinberg, if the question refers to allele frequencies (like "the frequency of the recessive allele is 0.4"), I would use the p + q = 1 (so in this case, the frequency of the dominant allele would be 0.6).

If the problem is referring to phenotypic frequencies or the number of individuals with a certain phenotype, I would use the p^2 + 2pq + q^2 = 1 equation. So for example, if the problem says the frequency of individuals with the dominant phenotype is 0.84, then that means p^2 + 2pq = 0.84 and, therefore, q^2 = 0.16. Another example, if the problem says that the frequency of individuals with the recessive phenotype is 0.01, then q^2 = 0.01 (so q = 0.1 and p = 0.9). If it says that the frequency of the homozygous dominant individuals is 0.64, then p^2 = 0.8.

As for determining the number of chromosomes and chromatids at a specific state...I would just draw it out in a simplified form. For example, if I'm given 2n = 46 and the cell is undergoing mitosis: I picture a scenario where 2n = 4 (or basically any small even number since its diploid), I draw out four << in a cell (where each << represents a chromatid pair). Then I picture the cell going through the stages of mitosis and separate the chromatids accordingly. Just remember that a chromatid becomes a chromosome at the very second that it separates from its sister chromatid. So, during anaphase of mitosis (where 2n = 4), you would have 8 chromosomes, so you have twice the number of chromosomes compared to 2n=4. So then apply that to 2n=46 and you get 92 chromosomes for anaphase!

If the cell is undergoing meiosis and 2n=4, I draw a total of two >><< (where << or >> represent sister chromatids; and >< represent homologs). And then once again, I separate according to the steps of meiosis. I hope this helps! I used to have some trouble with these questions until I started drawing them out in a simplified form like the one I've described.