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Unformatted text preview: Problem Set 3 1. Population Genetics (22 pts) I) Mutations (4 pts): define the following terms having to do with mutations in 15 words or less: 1 point per definition. The definition are <15 words each, so it’s rather loose. Deletion Loss of a segment of DNA from a chromosome. Nucleotide transversion Nucleotide substitution mutation where a purine is replaced with a pyrimidine, or vice versa. Missense mutation Mutation in DNA coding sequence that causes an amino acid substitution in the resulting polypetide. Frameshift mutation Mutation caused by insertions or deletions resulting a shift in reading frame of subsequent codons. 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. 1 point for each type of mutagen (agent capable of increasing the rate of mutations). There can be many examples of the individual types, so use your judgment to accept them or not. • Base analogues —like 5-bromouracil, an analog of thymine that is incorporated in thymine’s place and pairs preferentially with guanine. Simply—molecule that is incorporated into DNA in place of a normal base. • Nucleotide analogues —like base analogues, can be incorporated in place of a normal nucleotide. Examples are ddNTPs, 3’-Azido-2’,3’-deoxythymidine (AZT), etc. • Chemical agents —can react with DNA and change the hydrogen-bonding properties of the bases. Examples: nitrous acid (HNO 2 deaminates A, C, and G) and alkylating agents like EMS(ethyl methanesulfonate). • Intercalating agents —can insert between adjacent base pairs of DNA and cause misalignment between template and daughter strands of DNA. Examples—EtBr, proflavin. • Ultraviolet radiation —can cause pyrimidine dimers that block transcription and lead to inaccuracy of DNA replication. • Ionizing radiation —large doses increases overall rate of mutations. III) Gene pool (6 pts): a transversion in the second codon position for the sixth amino acid in the b- 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) 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? 2 points total, 1 for the definitions and 1 for the case specific question. • Allele fixation: when an allele’s frequency in a population reaches 1. • Heterozygote superiority: when the fitness(viability and/or fertility) of the heterozygote is greater than that of both the homozygotes....
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- Fall '02
- DNA, pts, amino acid sequence, ORFs