EvolutionTest2Ch9

• genetic variation: eg White and blue forms of snow goose caused by 2 alleles at same locus
• environmental variation: eg White (winter) and colored (summer) plumage in willow ptarmigan depends on season in which molt occurs

• ex- Human hair and skin color
• Multiple loci contribute to the continuous variation found in most phenotypic features (rather than multiple alleles at a single loci)
• Each contributing gene can have multiple alleles

• polygenic trait: traits which receive contribution from multiple genes
• *note- this allows for continuous variation
• pleiotropy: one gene affects multiple, seemingly unrelated, phenotypic traits

(p+q)²=p²+2pq+q²=1.0

• HW equilibrium describes genetic equilibrium of large sexually reproducing population (allele frequencies remain constant from one generation to the next unless acted on by outside forces)
• Mating is random (panmictic)
• Population size indefinitely large (removes effect of genetic drift)
• Genes are not added from outside the population (no gene flow)
• Genes do not mutate from one allelic state to another (no mutation)
• All individuals have equal probabilities of survival and reproduction (no natural selection)

You can contrast actual allele frequencies with HW expectations to determine if evolution is occurring in a population.  You may also be able to determine the rate of evolution by contrasting the current frequencies to expected frequencies.

• Mutation: random mutation in the genome
• Gene flow: exchange with other gene pools
• Genetic drift: Allele frequencies change randomly over time, alleles may be lost or fixed (increased intensity with smaller population size)
• Natural selection: Selective pressure against certain phenotypes inhibits reproductive success
• Non-random mating: mate choice, differential mating success, inbreeding

• inbreeding: mating between individuals with greater than average degree of genetic relatedness (self-fertilization is most extreme form)
• Population inbreeding typically results in a decrease of heterozygosity
• population inbreeding occurs that genetic similarity occurs regardless of lineage
• Inbreeding often results in an increase to homozygosity of deleterious recessive genes
• inbreeding depression: occurs when inbreeding causes decline in components of fitness (# bad alleles in pop is same, but genetic load is increased)
• *note-introduction of members of other populations may increase survival rate (European Adders, Golden Lion Tamarin in captivity)

• Polymorphic
• Phenotypic expression of many favorable traits leads to more offspring.
• NS acts on the sum of all traits, but each trait is effected differently.
• There is a graduation between those with all great traits and those with no great traits.
• A highly fit individual may still exhibit a bad trait.

• If 2 genes are located on the same chromosome their alleles are packaged into gametes together
• Since their alleles are inherited as a single unit, they are "linked"
• Linkage disequilibrium: refers to the population-level effects of linkage
• New alleles formed during meiotic recombination (D_t/D₀)
• LD will always decay to 0 in a population, and rate of decay is correlated with R (recombination)
• When R is .5 LD quickly approaches 0 (very few generations) - genes are far apart on chromosome
• When R is .001 LD very slowly (huge amount of generations) - genes are very close on chromosome
• *note-image on 238

• Variance in phenotype is the sum of genetic variance and environmental variance.
• *note- quantitative traits among individuals often fit a normal distribution; most useful statistical measure of variation is variance

• The proprotion of phenotypic variance due to genetic variance of a trait
• h2=V_G/(V_G+V_E)
• h² is equal to the slope of the regression line in a plot of mean value for all offspring vs Midparent mean

• Artificial selection can only be used to detect genetic variation if a trait is genetically heritable
• EX: selection for movement in response to light in Drosophila
• flies introduced at bottom of maze moved up, making successive choices between light and dark, and ending in 1 of 6 tubes
• 25 flies of each sex that had extreme + or - score were saved to start the next generation (they boned once they got to the final tubes)
• The selected populations diverged radically
• conclusion- genetic variation and heritability give the ability to evolve rapidly

• Panmictic: total random (blender) of entire species
• Very rare (ex Devil's Hole pupfish are in single sinkhole, Eels from eastern NA and western Europe migrate to one are near Bermuda to breed)
• Vast majority have subdivided populations
• sympatric: distinct populations with overlapping ranges comes into contact
• allopatric: distinct populations with adjacent (not overlapping) ranges come into contact
• parapatric: distinct populations with separate ranges (never come into contact)
• Subspecies: "geographic races"- recognizable distinct population that occupies a different area than other populations of the same spp
• (EX- 2 subspp of Northern flicker differ in color of wings, crown face, and size.  Have hybrid zone in midwest)
• (EX- 5 subspp of rat snake that differ dramatically in phenotype (color, pattern, etc).  Rarely interbreed, speciation on horizon?)

• Clinal variation: gradual change in a trait or allele frequency over geographic distance
• EX- body size in white-tailed deer (increase body size with increased lattitude over NA
• EX- Clines in frequency of F allele in alcohol dehydrogenase in fruit flies (decreased at lower latitudes in NA and Aus)
• Such clines illustrate that a trait is likely adaptive

• Ecotype: habitat-associated phenotypes
• very common in plants
• EX- ecotypic variation in sticky cinquefoil in CA
• plants cloned from several ecotypes grown in common gardens @ 3 altitudes
• flower color remained unchanged, regardless of altitude
• height diff. within each ecotype (at different elevations) reflects environmental effects
• height diff. among ecotypes (at same elevation) reflects genetic differences
• *image pg 247

• Bergmann's rule: Birds and mammals are larger in colder climates (because SA is decreased relative to body mass over which heat is lost)
• Allen's rule: Birds and mammals in colder climates have shorter appendages (reduces SA and heat is lost more slowly)
• Gloger's rule: Animal populations in arid climate are paler (match pale soil and vegetation to avoid predation)

• character displacement: sympatric populations of 2 species differ more than allopatric populations in various traits
• EX- bill size in seed eating ground finches in Galapagos island
• when the two finches reside on the same island there is very little overlap in the beak size (each is "specialized") but looking at the same spp on 2 different islands the bill depth has much overlap

• Gene flow: exchange of genes between populations
• carried by moving individuals (animals, seeds, spores) or gametes by wind, water or pollinators
• non-reproductive migration does not contribute
• Acts to homogenize populations (if there is gene flow among populations they will all eventually reach the overall average allele frequency)
• *graph is allele frequency (p) 0-1.0 vs # of generations.  No matter what value p is at generation 0 they become .5 (looks like a broom)
• *pg 248