3. Scientists determined the genotypes of 122 Havasupai people, a group of Nativ

Question

3. Scientists determined the genotypes of 122 Havasupai people, a group of Native Americans in Arizona. The two genes are located in the major histocompatibility complex (MHC), an important part of the immune system. The following data are the number of observed and number of expected people for the HLA-A and HLA-B genes. Observed Expected HLA-A Homozygotes Heterozygotes 38 84 48.43 73.57 HLA-B Homozvgotes Heterozygotes 21 101 29.56 92.44 Do the observed data significantly differ than expected? Why or why not? (NOTE: calculate each gene separately.) a. b. What might explain the relatively high frequency of heterozygotes?

Explanation / Answer

Ans A)

For HLA-A

Observed

AA=38

Aa= 84

Expected

AA= 48.43 (p2 x 122)

Aa= 73.57 (2pq x 122)

From this data,

the frequency of allele A= p= [(2 x 38)+84]/244 = p= 0.6557

the frequency of allele a= q= [84/122] = q= 0.6885

Now consider what the expected genotype frequencies would be, if the population is in hardy-weinberg equilibrium and compare these with the observed value.

these observed and expected values are differ significantly from those expected if the population is not in equilibrium.

Now take HLA-B

Observed

BB=21

Bb= 101

Expected

BB= 29.56 (p2 x 122)

Bb= 92.44 (2pq x 122)

From this data,

the frequency of allele B= p= [(2 x 21)+101]/244 = p= 0.5860

the frequency of allele b= q= [101/122] = q= 0.8278

Now consider what the expected genotype frequencies would be, if the population is in hardy-weinberg equilibrium and compare these with the observed value.

these observed and expected values are differ significantly from those expected if the population is not in equilibrium. These valve differ cosiderably, with same no of homozygous of both HLA-A and HLA-B in observed value. Heterogygotes have increased numbers than homozygotes in HW deviation.

Ans B)

Relative high frequency of heterozygotes found in HW deviation from part A calculation.Such as advantages or negative assortative mating, i.e. the attraction of opposites.

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