Allelic Frequencies

Ok, Question of the Day:
1. (5 pts.) Population Genetics Based Upon Phenotypes. Cyanogenesis in white clover, Trifolium repens, is controlled by two unlinked loci. One locus controls synthesis of a cyanogenic substrate while a second locus codes for synthesis of the enzyme that releases the cyanide radical from the substrate. Cyanogenic plants rapidly release cyanide when they are crushed. Cyanogenic plants can be identified by crushing their leafs in the presence of dinitrotoluene (I nitro away from TNT!) which turns red in the presence of free cyanide. The cyanogenesis phenotype is polymorphic in white clover populations throughout the world. Alleles at the first gene that encodes the cyanogenic substrate are usually fixed. Cyanogenic alleles are incompletely dominant to acyanogenic alleles at the second gene. Acyanogenic plants are assumed to be homozygous recessive. Numerous studies have shown that cyanogenic plants are eaten (by a variety of things) less often than acyanogenic plants. On the other hand, cyanogenic plants don't recover well from being trampled or crushed and generally show less vegetative growth and lower fecundity. The fitness of the genotype is thus dependent on the environment. You observe the following frequency of cyanogenic phenotypes in three populations. Assume the existence of two alleles at the second gene that encodes the enzyme that releases the cyanide radical.

Population 1 Population 2 Population 3
Cyanogenic

+ 0.2 0.5 0.95

- 0.8 0.5 0.05

a) Calculate the frequency of the cyanogenic allele in each population.

b) In two or three sentences provide a hypothesis to explain the maintenance of alleles at these frequencies in these populations. How would you test this hypothesis? (Hint: What selective forces might be operating in each of these populations?)


If anyone can tell me whether or not the part about incomplete dominance of the cyanogenic allele to the acyanogenic allele makes any difference at all, I will buy you a candy bar!!!! If you could also give me a better nudge in the right direction for question "b" that would be much appreciated and warrant an even better ICE CREAM CONE!!!

Ok, now that you all are on that...

It's Monday again, and I'm struggling with my homework. Also, unless my friend Emily comes to pick me up, I'm stranded on campus until 7:15, at which point we go over to the student center for an officer meeting, and then a team meeting at 8pm, meaning I will not get home until around 9pm. At which point I will have been on campus for a solid 12 hrs. Whoa.
Today was payday!!! I wasn't able to save anything this month, and probably won't be able to for the next two months, mostly because I have to make payments to CSU for my fees. I won't complain b/c certain people like to point out how cheap in-state tuition is vs out of state....but it's still a lot of money for me :)
Better get back to it, I have a bunch of homework still, and a tiny bit more lab stuff to finish up today if I can just buckle down.
Thanks for reading! Hope you all had a great Monday!

-Megan

ps. I forgot to mention trail work weekend #2! It went well, no one broke any bones...