Genetics Unit 12

population genetics

study of the genetic composition of biological populations and how those compositions changer overtime

single-nucleotide polymorphism

a change in a single position in DNA where one nucleotide is replaced by another; most basic and frequent form of variation

microsatellite loci

short sequence motif that is repeated multiple times with different alleles having different number of repeats

gene pool

sum total of all alleles in the breeding memebers of a population

gene frequency

the proportion of individuals in a popilation having a particular genotype

assortive mating

individuals choose mates based on resemblance of non-resembalance to themselves

gene flow

movment of alleles in or out of a population; can introduce new alleles or change ration of existing ones

mutation rate

probability that a copy of a allele changes to some other allelic form in one generation

subpopulations

small local populations

genetic admixture

mix of genes that results when individuals have ancestry from more than one subpopulation

genetic drift

allele frequencies change from one generation to the next as a result of chance when gametes are drawn from gene pool to form next generation

directional selection

changes the frequency of an allele in one direction until it reaches fixation or loss

balancing selection

natural selection that results in an equilibrium with intermediate allele frequencies

founder effect

drift caused by random sampling of the original population to create a new population

bottleneck

one or several generations of contractions in the population

locus

location within the genome

intergenic

SNPs between genes; typically neutral, acts as marker

intronic

SNPs within a gene’s introns, can affect mRNA splicing

regulatory

SNPs in the promoter, enhancer, or silencer regions; can alter the binding site for a transcription factor

synonymous

SNPs within a coding exon, changing the condon; neutral because the condon still codes for the same amino acid

non-synonymous

SNPs within a coding exon, changing the codon for coding for a different amino acid

missense

changes codcon to cone for a different amino acid

nonsense

changes codon to a stop codon

mononucleotide microsatellite

repeat unti is 1 bp

dinucleotide microsatellite

repeat unit is 2 bp long

trinucleotide microsatellite

repeat unit is 3 bp long; huntington’s disease

tetranucleotide

repeat unit is 4 bp long; DNA analysis

perfect microsatellite

motif repeats without interruption

imperfect microsatellite

motif is interrupted by one or more non-motif bases

compound microsatellite

two or more adjacent, distinct repeat motifs

Hardy-Weinberg law

mathematical model that describes a theoretical, non-evolving population in which allele and genotype frequencies remain constant across generations

G.H. Hardy and Wilhelm Weinberg

founders of Hardy-Weinberg equation

p

dominant allele

q

recessive allele

chi-squared test

test observed frequencies in Hardy-Weinberg

null hypothesis

no significant difference between the observed and expected results

alternative hypothesis

significant difference between observed and expected results

critical value

0.05

positive assortive mating

occurs when similar types of mates produce offspring

negative assortive mating

occurs when unlike individuals mate

inbreeding

mating between relatives

segregating sites

number of variable or polymorphic nucleotide sites in a set of homologous DNA sequences

number of haplotypes

simple count of the number of haplotypes at a locus in a population

gene diversity

probability that two alleles drawn at random from the gene pool will be different

mutation

source of all genetic variation

positive selection

brings favorable mutation to a higher frequency

purifying selection

eliminates deletrious mutations from a population