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 |