ps32002

ps32002 - Harvard-MIT Division of Health Sciences and...

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Problem Set 3 1. 1. Population Genetics (22 pts) I) I) Mutations (4 pts): define the following terms having to do with mutations in 15 words or less: ¾ ¾ ±±±±±± Deletion ¾ ¾ ±±±±±± Nucleotide transversion ¾ ¾ ±±±±±± Missense mutation ¾ ¾ ±±±±±± Frameshift mutation II) II) Mutagenesis (2 pts): what is a mutagen (in ten words or less)? Name two types of mutagens and briefly (in 20 words or less) explain how they cause genetic mutations. III) III) Gene pool (6 pts): a transversion in the second codon position for the sixth amino acid in the β -globin chain of hemoglobin is the recessive mutation responsible for sickle cell anemia. When the mutation is homozygous, it is lethal. However, people heterozygous for the sickle cell allele are protected from infection by the protozoan Plasmodium falciparum , which causes malaria. a) a) Define the terms “allele fixation” and “heterozygote superiority” in less than 20 words. Relate them to this case—in areas where malaria is a threat, would either allele become fixed? b) b) Let HbS + denote the dominant allele and HbS S the sickle cell allele. If in a certain population we find the following genotypic breakdown: Number of HbS + /HbS + individuals = 3915 Number of HbS + /HbS S individuals = 585 Number of HbS S /HbS S individuals = 0 What are the genotypic and allelic frequencies of the population in question? IV) IV) Hardy-Weinberg (10 pts): a 32 bp deletion in the gene coding for the human chemokine receptor CCR5, termed 32, is found to offer some AIDS resistance. The mutation of the membrane bound receptor hinders HIV infection of T cells. Here let’s denote the normal CCR5 allele as “A” and the 32 allele as “a.” Let’s say a 1000 person population was genotyped and we obtain 795 AA, 190 Aa, and 15 aa. a) a) There are around half a dozens of assumptions upon which the Hardy-Weinberg principle depends in order to have predictive value. Name three of these.
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b) b) Use the χ 2 test to determine whether the frequencies provided agree with those predicted by the Hardy-Weinberg law. 2. Monte Carlo Genetic Drift Simulation with Mathematica (10 pts) Consider a population of sexually-reproducing organisms with an allele A that has an initial frequency of 50%. In the absence of any randomness or other factors, the frequency would remain constant in successive generations. Here, you’ll use Mathematica to simulate what happens in a small population of organisms when gene
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This note was uploaded on 01/24/2010 for the course HST. 508 taught by Professor Dr.georgechurch during the Fall '02 term at MIT.

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ps32002 - Harvard-MIT Division of Health Sciences and...

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