Unformatted text preview: 204-325 1 Summary of the Last Lecture Extranuclear DNAs, including the mitochondria genome, chloroplast genome and some symbiotic bacteria and viruses follow rules different from the Mendelian inheritance of the meiosis based nuclear genes. Many but not all cases of extranuclear inheritance are maternal inheritance. Maternal effect refers to certain phenotypes of an individual that are determined by the maternal nuclear genome. Genomic imprinting results in a gene being differentially expressed depending on which parent it comes from.
2 Today's Topics 1. Genetic Structure of a Population: Genotypic Frequency, Allelic Frequency and Diversity 2. Hardy-Weinberg Law: Assumptions and Predictions
3 Topic 1 Genetic Structure of Population:
Genotypic Frequency and Allelic Frequency
4 Quantification of Gene Pool Genotypic Frequency = Number of Individuals with a Given Genotype Total Number of Individuals in the Population Allelic Frequency = Copy Number of a Given Allele Copy Number of All Alleles of the Gene in the Population 5 Allelic Frequencies for Genes with Two Alleles ( 2 X count of AA ) + ( count of Aa ) p = f (A) = 2 X total number of individuals ( 2 X count of aa ) + ( count of Aa ) q = f (a) = 2 X total number of individuals p = f (A) = f (AA) + q = f (a) = f (aa) + p+q=1
6 1 2 1 2 x f (Aa) x f (Aa) Allelic Frequencies for X-linked Genes with Two Alleles 7 Allelic Frequencies for Genes with Three Alleles 8 An Example of Genotypic Frequency Calculation 9 An Example of Allelic Frequency Calculation 10 Calculating Allelic Frequency from Genotypic Frequency 11 Measurements of Genetic Variations (Diversity) of a Population
Polymorphic locus = any locus that has more than 1 allele in whole population P (Proportion of Polymorphic Loci) = Number of Loci that are Polymorphic in whole Population Total Number of Loci Examined H (Heterozygosity) = Number of individuals that are heterozygous in a locus Total Number of Individuals in a Population
P is population specific; H is population and locus specific; For a population, average H for many loci is calculated.
12 Gel Electrophoresis 13 Electrophoresis of Hemoglobin Variants 14 Genetic Variations at Protein Level Loci in Loci in 15 Restriction Fragment Length Polymorphism (RFLP) 16 RFLP Patterns from Five Mice 17 Detection of STR Polymorphism by PCR PCR with primers X and Y and analyze by gel electrophoresis EtBr stained gel =PCR product size 18 Genetic Variations at DNA Level: Nucleotide Heterozygosity
average number of heterozygous nucleotides Hnuc = total number of nucleotides that are examined 19 Synonymous versus Nonsynonymous Substitutions Synonymous substitution = silent mutation (aa not changed) Nonsynonymous substitution = missense or nonsense mutation Heterozygosity 20 Topic 2 Hardy-Weinberg Law:
Assumptions and Predictions
21 Hardy-Weinberg law If a infinitely large, randomly mating population is free from mutation, migration and selection, then the allelic frequencies p and q do not change, and the genotypic frequencies are p2, 2pq and q2.
Important: Conditions are for the gene in question, not necessary for the individuals in question.
22 Punnett Square for a Population in gene pool Reach equilibrium in 1 generation (autosomal genes).
23 in gene pool Relationship of Genotypic Frequency to Allelic Frequency in Equilibrium 24 Algebraic Proof of Hardy-Weinberg Equilibrium 25 The Gradual Approach to Equilibrium for X-linked Genes
Female: Male: ( ) ( ) ( ) p(A) + q(a) 26 Summary Population genetics is the study of the genetic structure of populations and its evolution. Gene pool of a population is described by allelic frequencies. Distribution of alleles is described by genotypic frequencies. Diversity of a population is described by proportion of polymorphism and by heterozygosity. The Hardy-Weinberg law states that if a large, randomly mating population is free from mutation, migration and selection, then the allelic frequencies p and q do not change, and the genotypic frequencies are p2, 2pq and q2.
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