Life Science: Human Genetics CORE-UA 303 Homework Assignment 8 [10 points total] Population Genetics

Life Science: Human Genetics CORE-UA 303 Prof. D. Fitch Homework Assignment 8 [10 points total] Population Genetics 1. [4 points] Lactose intolerance (due to "lactose malabsorption") is recessive. The abstract of one study (Wang et al., 1984, Human Genetics 67(1):103-106) reads as follows: "Lactose absorption capacity was examined in 641 apparently healthy adolescents and adults (447 males and 194 females with an average age of 22.9 years and an age range of 16-46 years) using a field version of the lactose tolerance test with breath hydrogen determination. In the total sample, 89 lactose absorbers and 552 lactose malabsorbers were identified. Lactose malabsorption was most frequent in a subgroup of Han (Chinese) from northeastern China (229 of 248 subjects, 92.3%). Among 198 Mongols from Inner Mongolia, there were 174 lactose malabsorbers (87.9%). The frequency of lactose malabsorption was lowest in a group of Kazakhs, traditional herders from the northwestern region of Xinjiang (149 of 195 subjects, 76.4%). Reported symptoms of lactose intolerance were significantly more frequent in lactose malabsorbers. The findings in northern Han are similar to the reported lactose malabsorption frequency in southern (mainly overseas) Chinese, and correspond with the absence of animal milk from traditional Chinese diets. The relatively low prevalence of lactose malabsorption among the Kazakhs suggests that lactose persistence may be frequent in herding pastoralist populations of southwest Asia." a. The variant site that causes this difference between alleles is not located in a transcribed region of the lactase gene. How could it cause lactose intolerance? b. Under the assumption that the populations are in Hardy-Weinberg equilibrium, calculate the expected frequency of each of the three genotype classes at this locus among the following populations: Population f(TT) (tolerant) f(Tt) (tolerant) f(tt) (intolerant) Han Mongol Kazakh Total c. The authors suggest that (1) lactose malabsorption is "relatively low" for Kazakhs and that (2) this may be due to "lactose persistence". Do you agree with the assessment that lactose malabsorption is significantly lower in the Kazakh population than in the total population set? Back up your conclusion with chi-square statistical analysis. Hint: a null hypothesis would be that the Kazakh population is a random sample of the combined, Total populations, i.e. the expected frequency of tolerant phenotypes = f(TT) + f(Tt) and the expected frequency of intolerant phenotypes = f(tt). You can use the "Chi-square test of phenotype ratio" in the Chi-squareC file provided. If you agree with the authors, how could lactose persistence (i.e., lactose still a major part of diet) cause this difference in genotype frequencies? 2. [1 point] Why is heterozygosity lower in people w