Can you please help me with this?

Question

BIOLOGY 1108 EVOLUTION AND POPULATION GENETICS

Variations on the ability to taste PTC have no obvious survival value, and yet there is ethnic variation in allele frequencies between different groups. For instance, 63% of Arabs are tasters for PTC, whereas 63% of native Americans can't taste it. At least one condition of the Hardy-Weinberg Theory was not met respect to the gene in the world populations.

1. How do you think this ethhnic variation came about?

2. How could this variation in allele frequency be associated with survival potential of the ability to detect a bitter taste?

3. Assuming there was no selective advantage for this traitt, what other factor might account for the ethnic differences?

This is my homework. Its not for a grade for right or wrong but for effort and I am having a little trouble with this. Does anyone know about this stuff if so please help me. Even though the grade is for effort I still want to understand it so I'll do good on the test. Thank you

Answer 1

I'm basing this *entirely* on the information given in your question. E.g. I don't know what the percentages for PTC tasting in other parts of the world between the middle east and N. America, or what food stuffs might contain PTC or whether they were otherwise harmful or beneficial. To your 3 questions:

1. The ethnic variation might be explained by migration histories, and the time of appearance of the PTC allele in the population. This would need to be verified by the percentages found in other populations along the believed migratory paths of N. American natives.

2. It could have survival advantages it it allowed the posessors to avoid some harmful foods (e.g. some plant or spice with long-term health problems). In those regions where this plant existed, those with the allele might have a distaste for this type of food, and therefore eat less of it, and the allele would grow in population. In regions in which the plant did not grow at all, the allele would have no advantages, and might stay fairly infrequent.

Or alternatively, if some beneficial foods contained PTC in a way that made them tasty to the possessor of the allele, then the frequency of the allele in the population might encourage more of that food in the diet of the culture ... i.e. it would have benefits even to people who did *not* have the allele, and therefore couldn't taste it. Or, perhaps (silly example) if those few foods that contained PTC also had aphrodisiac properties, then this would have obvious advantages as far as propagation of the allele that made those foods attractive. So populations that contained more "PTC-tasters" would tend to live longer and bred more. Populations with fewer "PTC-tasters", or who lived in regions in which PTC-containing foods did not exist, would not live as long.

3. The most likely explanation is that the gene location for the allele might be close to the gene location for some other gene that did have regionally determined survival advantages. The PTC allele just is along for the ride.

Answer 2

I think in the case of the ability to taste PTC, that it is likely that there is occurring what is known as a "founder effect". Since the amount of genetic heterogeneity in the world populace is a function of recent vintage (There wasn't very much large scale migratory behavior of humans prior to the 19th century), the change in allele frequency to approach "equilibrium" might very easily have not yet been reached. In the absence of a viable survival phenotype associated with the particular gene, it would be hard to suggest a "positive pressure" for maintaining this gene. The same could be said for the occurrence of "tongue-rolling" ability in a given population.

Answer 3

Hi. Your question is complicated and requires a lot of reading. However my suggestion is as follows: I use the search engine metacrawler.com (best search engine). Simply type in "PTC taste allele frequency". That search gave me lots of hits, especially informative was htpp://sps.k12.ar.us/massengales/population_genetics_and_evolutio.htm
If you want to get more into it try the Science Magazine at www.sciencemag.org Select All HighWire Journals on the top right so you can search all international scientific publications, then type in your search. That should give you plenty of information but you have to dedicate some time to this proyect, it seems complex. Good Luck.

Answer 4

Well for starters, it could be closely linked to a trait that has some survival value. That way it would be incorporated disproportionally into different populations.

Secondly, it could be attributed to random genetic drift. I suggest reading the wikipedia entry for genetic drift. I hope it helps ;)

http://en.wikipedia.org/wiki/Genetic_drift

Answer 5

Don't forget about the requirement for Hardy weinberg Theory....
Hehehe