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Genetics help


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Genetics help

Postby AdamH » Tue Aug 23, 2011 11:20 pm

So there is this assignment where I am having a bit of difficulty in understanding the questionings. I've been given a set of data related to the phenotypic expression of dominant or recessive genes (eg: PTC tasting - 27 positive and 61 negative, Atchoo Syndrome - 15 positive and 73 neg, etc..etc..)

Now I have been firstly asked to find the relative frequencies of each individual phenotype. Which I believe is simply the data over the total poulation so, for PTC it would be 27/88 and 61/88 = 0.31 and 0.69 respectively.

The enst question however asks me to use these frequencies to calculate the proportion of the population that has a “no” score for every character. Does this mean I need to find their no score percentage? i.e for PTC (61/88)*100?

Additionally it asks to assume that the frequencies are representative of an X country's population and if so how many people in country X have the same phenotype as myself (use a population size of 20 million and explain your calculations).

For this I can work out my own phenotype but I am unsure of how to calculate this question. Since the sample frequencies are from a population of 88, do I simply scale it to 21 million and find the frequencies for my phenotype?

Any help in clarification would be greately appreciated.
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Postby canalon » Tue Aug 23, 2011 11:43 pm

I would say you are correct for 1 and 2 and for the lest question you just multiply your frquency (say 0.39) by the population (20 or 21 million) to have the number of PTC tasting people (7.8 million for 20 million people).
Assuming that you taste PTC :)

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Postby AdamH » Wed Aug 24, 2011 12:15 am

Thanks Canalon for clearing that up for me :)

One last thing if I may, one question asks:
PTC tasting is dominant to non-tasting. Assuming the class is in Hardy-Weinberg
Equilibrium, what is the frequency of the tasting allele in the class?

I dont fully understand how HW would bear a relavance on a population so small and essentially only in one generation.
I can see that PTC tasting would be = f(AA) {dominant to non-tasting} = P^2. This in turn is = 0.69 as it is the relative frequency of the no score. So..to find the tasting allele do I just simply 1-(p^2)? or have i gone about it wrong?

Thanks again for the help.
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