Thursday, September 20, 2007

Measuring Evolution of Populations

Measuring Evolution of Populations.

Hardy-Weinberg formulas:
The formula for alleles is p+q=1. We must assume that there are two alleles. p is the frequency of the dominant allele, and q is the frequency of the recessive allele. The frequencies must add to one, therefore p+q must equal one. The formula for individuals is p²+2pq+q²=1. p² is the homozygous dominant frequency. q² is the homozygous recessive frequency, and 2pq is the heterozygotes frequency. The frequencies must add to 1, so p²+2pq+q² will equal one.

Sickle cell anemia:
Sickle cell anemia is very painful as well as it can be fatal. It strikes 1 in 400 African Americans, which is a lot! Sickle cell anemia is a mutation in the gene coding for hemoglobin, which is what carries oxygen in red blood cells. The recessive allele is H^s H^s, and the normal allele is H^b. When a person has sickle cell, what is happening is the red blood cells are breaking down, and instead of being round cells they become crescent like shapes and cannot flow smoothly. Therefore, blood vessels get clogged and organ damage occurs. This can be very painful.
Sickle cell has the highest frequency in heterozygotes(H^b H^s). 1 in 5 central Africans, which is a huge number, are heterozygotes. 1 in 100 are homozygous. They usually die before their reproductive age. Since the H^s allele has such a high level in the African population, it suggests that there was an advantage of being heterozygous.

Malaria is also common in Africa. It is caused by a mosquito bite which contains a single celled eukaryote parasite, that spends part of its life in red blood cells. It basically goes from the mosquito into the humans blood stream, it then goes to the liver to mature and reproduce, and then goes to the red blood cells where it eventually bursts them open. The person will those thousands of blood cells, get a high fever, and can sometimes die.

Advantage for Heterozygotes:
In Africa, homozygous dominant (H^b H^b) die of malaria, homozygous recessive (H^s H^s) die of sickle cell anemia, and heterozygote carriers (H^b H^s) are mostly free of both. This gives a huge advantage to heterozygotes, and could be good explanation for an excessive amount of heterozygotes in Africa. They are the ones surviving.

This is what we went over today. It wasn't too hard, but if you need help just ask.

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