Population genetics

Description:	Stack #174010
Category:	Genetics
Created by:	knpearso on 2008-11-07

Question	Answer
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