hardy-weinberg question

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thewax
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hardy-weinberg question

Post by thewax » Mon Jan 05, 2009 2:37 am

Note: This is not a homework question. This is preparation for an upcoming test.

Question: Why are there most of the time/ sometimes values of the allelic frequencies that are not 50%, 25%, or 75%???????????? I mean, if you do the punnett square, you don't get values like 0.6 or 0.4 - you get something like 50%, 25%, 75%, 100%, 0%, etc. but you don't get 0.6 or 0.4 (or any other values, for that matter)????????? I mean, isn't it RANDOM???????????

Progress on this question: I looked all over the place (books, websites, etc.) and still couldn't find the answer. Could anybody help me?????????????????????????????????

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alextemplet
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Post by alextemplet » Mon Jan 05, 2009 4:54 am

A punnett square only describes the statistical outcomes of crossing two individuals. Allelic frequencies describe how common certain alleles are through an entire population.
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thewax
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Post by thewax » Mon Jan 05, 2009 5:30 am

Thanks! :)

So to clarify - are you saying that the punnett square and the allelic frequencies are completely separate things???????

So when in the Hardy-Weinberg equations, you square the p - p^2 - and the q - q^2 - I got pretty confused because it seemed pretty similar to the punnett square. :oops: I'm sorry I didn't post a better question, although the one I posted was a part of my question. Could anyone help????????

Wait, if I apply what you said, it might make sense. In the punnett square, you know the two individuals you are crossing, so you know their specific genotypes. However, in the allelic frequency, when you square the variables, you are basically trying to not predict the probabilities of the specific genotype of a cross between two individuals (as that's for a Punnett square), but you are trying to find the average/expected FREQUENCY of a genotype (i.e. AA, Aa, or aa) if there is RANDOM MATING - a condition essential for the Hardy-Weinberg equilibrium - and THERE IS COULD BE MORE THAN ONE MATING (ALTHOUGH ONE MATING IS OKAY, TOO) and you are just trying to find the expected percentage ACROSS THE POPULATION that when you conduct a random mating, you will get a particular genotype. So I guess what I'm really trying to say is that in allelic frequency, when you square the terms, you are trying to find the expected percentage (across the population) that when you conduct a random mating, you get a particular genotype. But, however, in the Punnett square, the mating is NOT random so you know the parents' genotypes and you want to find the probability of a particular genotype. So I guess it really boils down to the fact that Punnett squares deal with individuals and non-random mating to allelic frequency where you deal with random mating throughout the whole population. Right???????????????????????????????????

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Post by alextemplet » Mon Jan 05, 2009 5:04 pm

You've got it! ;)

Another way to look at it is that the punnett square tells you what happens when you cross two particular genotypes, whereas allelic frequencies tell you how common those genotypes are in a given population.
Generally speaking, the more people talk about "being saved," the further away they actually are from true salvation.

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Post by thewax » Wed Jan 07, 2009 2:00 am

A very nice, succinct way of summarizing what I said. :)

THANKS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! :)

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