Ap Biology Lab 8

Fluck 1 Alysa Fluck Mrs. Humphrey AP Bio Period 9 16 Monday, 2009 AP Biology Lab 8 Purpose -

Learn about the Hardy-Weinberg law of genetic equilibrium

-

Study the relationship between evolution and changes in allele frequency by using your class to represent a sample population

Data (See attached) Analysis Exercise A Populations Class North American

Phenotypes Tasters (p2 + 2pq) # % 16.000 0.670 0.550

Non-tasters (q2) # % 8.000 0.330 0.450

Allele Frequency Based on the H-W Equation p q 0.426

0.574

0.329

0.671

1. What is the percentage of heterozygous tasters (2pq) in your class? The percentage of heterozygous tasters in our class is approximately 0.489. 2. What percentage of the North American population is heterozygous for the taster trait? The percentage of heterozygous tasters in North America is approximately 0.4417. Exercise B Allele Frequency: The allele frequencies, p and q, should be calculated for the population after five generations of random mating.

Fluck 2 Number of A alleles present at the fifth generation Number of offspring with genotype AA

2 x 2 = 4 A alleles

Number of offspring with genotype Aa

12 x 1 = 12 A alleles Total = 16 A alleles

P = total A alleles / Total alleles in pop. (# students * 2) = 16 / 42 = 0.381 Number of a alleles present at the fifth generation Number of offspring with genotype aa

7 x 2 = 14 A alleles

Number of offspring with genotype Aa

12 x 1 = 12 A alleles Total = 26 A alleles

P = total A alleles / Total alleles in the population (# students * 2) = 26 / 42 = 0.619 2. What does the Hardy-Weinberg equation predict for the new p and q? According to the Hardy-Weinberg equation, our p and q values should equal 0.5. 3. Do the results you obtained in this simulation agree? If not, why? Our results vary from the expected results, mostly because we did not fulfill all of the assumptions for the Hardy-Weinberg equation. 4. What major assumptions were not strictly followed in this simulation? It was assumed that the population size would be much larger than the one that we sampled. Therefore, the percentages do not completely come into play. Case II 1. How do the new frequencies of p and q compare to the initial frequencies in Case I? In Case 2 p = 0.83 and q = 0.17. These numbers are very different than the initial frequencies. They are much different than the expected numbers.

Fluck 3 2. What major assumption(s) were not strictly followed in this simulation? The assumption that there is no natural selection was violated because when the aa genotypes were received they died. This selection greatly changed the data and that is why there is not a genetic equilibrium. 3. Predict what would happen to the frequencies of p and q if you simulated another five generations. I think that the data would become heavier in the AA genotypes because a homozygous recessive genotype is much harder to continue through generations. The p value would increase and the q value would decrease directly. 4. In a large population would it be possible to completely eliminate a deleterious recessive allele? No because there will always be the recessive allele present in carriers of that trait. The natural selection can not destroy that trait entirely because the carrier does not express it and is not weekend by the trait. They may still pass it on to their offspring if the offspring was a carrier. Case III 1. Explain how the changes in p and q frequencies in Case II compare with Case I and Case III. The values from Case II are different from case I in that the p value is much higher and the q value is much smaller. Compared to case III the p value is still higher in case II. In case II, the AA offspring were able to survive automatically so that allowed for more A alleles than a alleles because there were a smaller amount of heterozygous offspring. 2. Do you think the recessive allele will be completely eliminated in either Case II or Case III? I think it would be impossible for the recessive allele to be completely eliminated because in Case II the allele is hidden in the carriers and will still continue to be passed on in offspring

Fluck 4 carriers. In Case III, the carriers of the recessive allele are favored by the natural selection, so they also will pass on the trait. 3. What is the importance of heterozygotes (the heterozygote advantage) in maintaining genetic variation in populations? The heterozygotes allow for genetic variation. This creates more phenotypes which can better suit specific environments. Case IV 1. Explain how the initial genotypic frequencies of the populations compare. The initial frequencies differed only slightly from each other. 2. What do your results indicate about the importance of population size as an evolutionary force? The smaller the population, the greater the variance in the allele frequencies because there are fewer options to mate with. Hardy-Weinberg Equation Problems 1. In Drosophila the allele for normal length wings is dominant over the allele for vestigial wings (vestigial wings are stubby little curls that cannot be used for flight). In a population of 1000 individuals, 360 show the recessive phenotype. How many individuals would you expect to be homozygous dominant for this trait?

2. The allele for unattached earlobes in dominant over the allele for the attached earlobes. In a population of 500 individuals, 25% show the recessive phenotype. How many individuals would you expect to be homozygous dominant and heterozygous for this trait.

Fluck 5 3. The allele for the hair pattern called Widow’s peak is dominant over the allele for no widow’s peak. In a population of 1000 individuals, 510 show the dominant phenotype. How many individuals would you expect of each of the possible genotypes for this trait?

4. In the U.S. about 16% of the population is Rh negative. The allele for Rh is expressed to the allele for Rh positive. If the student population od a high school in the U.S. is 2000, how many students would you expect of the three possible genotypes?

5. In certain African countries, 4% of the newborn babies have sickle-cell anemia, which is a recessive trait. Out of a random population of 1000 newborns babies, how would you expect for each of the three possible genotypes?

Fluck 6 6. In a certain population, the dominant phenotype of a certain trait occurs 91% of the time. What is the frequency of the dominant allele?