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Population genetics

Stack #174010

population genetics Study of the distribution of alleles in populations and the factors that alter the frequency of alleles and genotypes
significance of population genetics Gene discovery, Genetic counseling, Planning population screens,
allele The alternative forms of a gene or DNA sequence.
What does an individual possess at autosomal locus? two alleles, one inherited from their mother and one from their father.
SNPs are the main source of human genetic variation
Types of alleles SNPs, Short insertion/deletions, and Copy Number Variants
characteristics of SNPs One nucleotide change, frequent, 1/1000 bp,
“functional” SNP contributes to phenotype
examples of short tandem repeats short tandem repeats as in Fragile X, Huntington Disease
haplotypes Combinations of alleles at separate loci. on the same chromosome but at a distance where recombination does not occur freely
In general the number of haplotypes is 2n, where n is the number of loci with two alleles each
Polymorphisms-definition sum of the least common allele exceeds an arbitrary setpoint of 1%
Polymorphisms arise when mutations increase in frequency in populations as a result of selection pressures or random genetic drift
If haplotype loci are very close haplotypes may exists in a population at a frequency higher than would be expected with independent segregation
diseases can be associated with alleles or haplotypes
copy number variants (CNVs) Result from non-allelic homologous recombination-Common source of variation (~10%)
hardy weinberg law allows one to calculate the frequency of alleles in a population if their genotype distribution is known or go from distribution of genotypes to compute allele frequencies
hardy weinberg assumes 1. population is large and mates randomly 2. no new mutations 3. no selection against genotypes 4. no mixture with population with different allele frequencies
disruptions of H-W suggests one of assumptions incorrect
both selection and genetic drift can affect the frequency of an allele or haplotype population
migration and bottlenecks results in some populations having higher frequencies of deleterious alleles that characterize them for certain disease risks
Grouping of human populations can predict genetic variation
Typographical race (skin color)
Discontinuous ethnic (culture)
clinical geography
Allele frequency Fraction of total population that carries a particular allele
Most human genetic variation occurs as SNPs and most SNPs only have two alleles
The sum total of allele frequencies in a population must be 1. Therefore
Humans are diploid so how may genotypes possible there are three possible couplings or genotypes from a two allele SNP
Hardy-Weinburg equilibrium p2 + 2pq + q2 = 1 (where p + q = 1) Use in estimating heterozygote frequency for rare alleles
If q2 is small (< 1/1000 then q ~ 0 and p ~ 1) Then the heterozygote frequency
genetic drift frequency of allele varies from one generation to the next
Non-random mating stratified populations
Stratified population has sub-groups that are genetically isolated within the larger population. e.g. the Amish in US
Assortative matings genetically isolated based on choosing a mate with a specific trait or background. e.g. race
Consequences of Consanguinity 1) Directly affects GENOTYPE frequency (more aa than expected)
mutation rate: one chance in a million of having a child with new mutation 2) Cause: faulty replication
Biological fitness is a measure of fertility..f = 0; genetic lethal mutation causes infertility or death prior to reproductive period f = 1; no effect f > 1; a phenotype (and its genotype) selected for
genetic disorders with f<1 direct effect on allele frequency
f<1 Why doesn’t the frequency of these diseases decrease? High mutation rate; To be stable in the population the severity of the selection is offset by the mutation rate
Created by: knpearso

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