Genetics - Population genetics

F factor

- 1/2 for self fertilization - allele frequency stays the same --> genotype changes - smaller it gets less genetically similar you are - put F factor into Hardy Weinberg by placing it in front of pq - homozygous p^2/q^2 + Fpq - heterozygous = 2pq - 2Fpq --> more F takes away more heterozygotes

Population

- a group of individuals of the same species that can interbreed with one another

Migration

- also referred to as gene flow - influx of alleles from another population - changes HW equilibrium - increases genetic variation between two populations - prevents genetic divergence between two populations - increased gene flow between species makes them more uniform - migration can reduce the number of recessive homozygotes phenotypes - can reduce harmful alleles as well

genetic drift

- changes in allele frequency due to random events - not large populations are infinity large - independent decisions affect frequencies of next generations - more pronounced smaller the population - cant be modeled --> random events - s^2 = pq/2N --> predicts how widely frequencies will vary from HW based on variance - smaller N = higher variance from equilibrium - s^2 = standard deviation of allele frequencies N = number of people in population

chi squared for allele frquency

- degrees of freedom = 3 genotypes - 2 alleles = 1 df

Natural Selection

- determined by individuals fitness - a genotypes ability to survive (viability) and reproduce --> pass on genes to next generation - directed forces -

mutation

- direct change to alleles - increased genetic variation - happens at a constant low rate - not sufficient to make a big change to allele frequency alone --> needs help from selection - de nova mutations --> new spontaneous change

Founder Effect

- establishment of a large population from a small number of individuals - small pop go and colonize new environment - genetic diversity only reflects few initial colonizer - much of diversity is in Africa --> every migration away resulted in more and more founder effects --> different genetic diversity for different sub populations

stabalizing selection

- genetic diversity decreases - population stabilizes around one particular trait - traits do not change drastically over time - selects against extremes

consanguineous mating

- inbreeding - F = coefficient for inbreeding --> measures how closeley related two mates are - measure of probability that two alleles are identical by descent - based on genetic similarity - changes genotypic frequencies - increases homozygosity - homozygosity is a problem --> increases chance for homozygosity for deleterious mutation - small populations become inbred much faster

Selection

- inverse of fitness - 1 - W =s -s = selection - used to model HW equation - selection against dominant allele = fast --> immediately at disadvantage from birth - selection against recessive = fast at first, but then slow and protected by heterozygotes --> homozygous recessive still quickly killed - can have selection against both homozygous alleles --> sickle cell --> resistance against malaria, without sickle cell --> hetero --> two opposing forces

Population genetics

- looks at whole populations genetics

Polymorphism

- many traits display variation within a population - at least 2 alleles for a trait

dissasortative mating

- mate preference for different traits - -1 value = completely disassortive - 0 = complete randomness - pushes toward heterozygosity

assortative mating

- mate preference for similar traits - 1 value = completely assortative - pushes for homozygosity

m

- migration - frequency of allele a in population 2 after migration is q'2= q1m + q2(1-m) - m = % of new population from migration q1 = allele frequency in population 1 q2 = allele frequency in population 2 - q'2 = new frequency of allele in population 2

things that change ideal equilibrium

- non random mating - mutations - genetic drift - migration - natural selection

hardy weinberg equation

- p^2 + 2pq + p^2 - based on the punnet square - p + q -1 at equilibrium... - allele frequency stay the same - genotype frequency stays the same - alleles passed on to generation to generation through different genotypes --> passed on with same freqeuncy - use chi squared test to see if a population follows the ideal frequencies

directional selection

- pushes traits toward one extreme that gives best survivability - shifts toward one phenotype

Bottle Neck effect

- random elimination of most members of a population without regard to genetic composition --> disaster - newly reestablished population will have less genetic variation - initially large diverse population decreases, then increases again but new population will be less diverse

lactase persistance

- resulted from 1 SNP in Europe

disruptive selection

- selects against heterozygotes - pushes for two distinct different traits - leads to speciation

neutral genes

- small difference between observed and predicted frequencies

gene pool

- total number of all alleles carried in all member of a population - small isolated populations of different species around world with different mutations and different selecting factors

Hardy Weinberg equilibrium

- used to model the relationship between allelic and genotypic frequencies in populations - based on ideal population --> many necessary rules - no migration - random mating - no natural selection - no mutation - very large population --> infinitely large

genetic divergence

- when two populations of ancestral species accumulate mutations over time and become reproductivly isolated - speciation eventually occurs - lack of gene flow between these populations make these species allele frequencies unique - seperated by environmental factors

Genotype Frequency

Number of individuals with a certain genotype in a population / Total number of all individuals in a population

Fitness W

average # of offspring of a given genotype by the average # of offspring produced by the most prolific genotype - ranges from 0 -1 - can measure over generation - relative fitness for each genotype

Allele frquency

number of copies of an allele/ total number of alleles for that gene - can also use genotypic frequency to calculate p and q - p = dominiant allele --> dominant homo frequency + 1/2 hetero frequency - q = recessive allele --> homo recessive + 1/2 hetero frequency - however can do reverse --> from allele to genotype frequency - need to know at least two frequencys

mutation frequency

u = mutation frequency --> probability that a gene will be altered by a new mutation - change in allele frequency Aq = up change in q is recessive allele - subtract change in q from p, and add to q - main effect in dominant lethal genetic disease--> rarely reproduce --> de nova mutations --> only driving force of these rare mutations