Introduction to Genetic Analysis (Introduction to Genetic Analysis (Griffiths))

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Chapter 17 Chapter 17: Population Genetics I) Genetic composition of a population is the collection of frequencies of different genotypes in the population A) Consequence of processes that act on individual organisms to increase/decrease the number of organisms in the genotype 1) Mating patterns 2) Migration 3) Mutation 4) Recombination 5) Natural selection 6) Random fluctuations—genetic drift B) Study of variation 1) Description of the phenotypic variation 2) Translation of phenotypes into genetic terms a) Genotype frequencies—list of observed proportions of genotypes in a population b) Allele frequency—frequency of the alternative alleles, proportion of what allelic form of the gene among all the copies of the gene in the population i) Each individual diploid is counted as contributing two alleles ii) p=frequency of wild type= f A/A + ½ f A/a q=frequency of alternate allele= f a/a + ½ f A/a = 1-p II) Protein polymorphisms A) Immunologic polymorphisms—antibody, always n(n-1)/2 ways of combining n different things two at a time B) Amino acid sequence polymorphisms 1) variation in the amino acid sequence of a protein can be detected by sequencing DNA 2) Also detect variant proteins by gel electrophoresis a) Makes use of change in the physical properties of a protein when one amino acid is substituted for another b) Detects the change in net charge on the protein c) Allows for the study of proportion of all structural genes in the genome in a species is polymorphic and what average fraction is in the heterozygous state i) 1/3 of genes are polymorphic ii) 10% is average heterozygosity III) Sequence polymorphisms A) Chromosomal polymorphisms B) Restriction site variation—Restriction Fragment Length Polymorphism (RFLP) 1) Polymorphisms in the restriction sites will cause different lengths of DNA fragments 2) Single-base pair changes that destroy restriction enzyme recognition sites or in-dels in stretches of DNA b/t locations of restriction sites will cause restrion fragment lengths to vary C) Tandem repeats—Variable number of tandem repeats (VNTRs) 1) Arise from the occurrence of multiply repeated DNA sequences 2) Short sequences of DNA are dispersed throughout the genome and is repeated in a row 3) Number of repeats of these stretches vary (VNTR) 4) If restriction enzymes cut sequences that flank either side of tandem array, a fragment is produced that is proportional to the number of repeated elements D) Complete sequence variation—Single-nucleotide polymorphism (SNP) 1) Variation in the nucleotide at a single position 1 of 5
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Chapter 17 2) Can be studied: a) In protein-coding regions of the genes i) Can be translated to reveal exact amino acid sequence differences in proteins ii) DNA sequencing is superior to electrophoretic studies of the protein—can identify what amino acids are differing iii) Different regions of the same protein have different amount of polymorphisms b) In base pairs that do not determine or change the protein sequence—i.e.
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Chapter 17 - Chapter 17 Chapter 17: Population Genetics...

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