What’s genetic drift?
Random chance fluctuations in allele frequencies w in a pop over time, most strongly in small populations, net result of good and bad luck causing random changes in allele frequencies due to chance, random sampling error
What does genetic drift result from?
Random sampling error, more genetic drift in smaller populations
Key points of genetics drifts relation to populations?
Tends to reduce genetic variation w in pop, increases genetic variation BW pops, strongest in smaller pops (bottleneck and founder events), amuses allele frequencies to randomly change in population -> evolution, causes population divergence-> fixed or lost traits
Why is genetic drift stronger in smaller pops?
Going to reach less genetic variation/fixation in fewer generations
What is the genetic drift example of the northern elephant seals?
Underwent a bottle neck in late 1800s due to commercial hunting, numbers reduced to ~20-100, all in one breeding ground in Mexico, post bottleneck more likely to be homozygous at any given locus (know from sequencing dna from 1000 year old seal bones), more homozygous deals have lower fitness (inbreeding depression), hunting stoped and abundance increases to >200 000 today, reduced genetic variation didn’t prevent recovery in this case but they lost diversity
What’s the bottleneck effect?
Sharp drastic reduction in size of population caused by environmental events (earthquakes, floods, fires) or human activities (hunting, habitat destruction), type of genetic drift that causes reduced genetic diversity leaving small random assortment of survivors w limited genetic variation
What’s the founders effect?
Type of genetic drift (special case of bottlenecks and genetic drift) new isolated population is established by a very small number of indv from larger original population, carries only fraction of og pop genetic diversity, less diverse alleles, lost of diversity b/w diff founders pops though due to sampling error
Founder events in human history?
Phylogeny, human pops are closely related to geographical neighbours, all non-African descends from small population of humans which lived in Ethiopia, decline in genetic diversity reflects founder effects as you move further out
How does the founder effect explain the elevated prevalence of Ellis-van creveld syndrome in the old order Amish in Pennsylvania, a genetically-based health condition?
Rare recessive allele was carried by one of the 200 founded of the community In the 1700s, mostly married each other (figurative island pop), symptoms include polydactyls and other skeletal anomalies, 1/5000 Amish vs 7/1000000 in gen, other historically isolated human pops elsewhere have incidence of other genetically based phenotypes (10% colour blindness in pingalep island in Micronesia, typhoon wiped most of pop), genetic drift causes more homozygosity w/I pop and more genetic variations b/w pops.
Sockeye salmon and bears as an example of genetic drift?
Salmon (male)bigger and deeper bodied in bigger streams where there less bears due to predation , body depth corisponds with water depth due to narrower streams being easier for bears to grab salmon to eat them as bears for gating at breeding sites select bigger deeper bodied salmon to prey on there for select for male salmon (sexual dimorphisism)
What are the conditions for evolution by natural selection?
Indv in pop must vary in phenotypes, survival and reproduction not random but associated with indv phenotypes (selection), variation is based on to offspring (inheritance), heritable variation increases fitness
What are the four types of selection that show the relationship between phenotypes and fitness?
Directional, stabilizing, disruptive and frequency-dependent selection
When fitness is independent of phenotype how’s selection?
No sleection, condition for HWE, nothing is selected for
What’s directional selection?
Evolution of trait mean, occurs when fitness increases or decreases as the trait increases, ex. Bear predation or CURE project,mean shifts right or left on graph, diagonal line for fitness
What’s stabilizing selection?
Average indv have higher fitness then extreme indv, variance decrease b/w generations but the trait mean doesn’t change, more curved graph and squeezed together, curve line for fitness, peak at mean ex. Gall size in gall wasps
How does stabilizing selection work in gall wasps?
Trade off b/w repro and survival, extremes traded against, max number of offspring (increased size of gall) vs max survivabilty (decreased size of gall due to predation via bird)
What’s disruptive selection?
Both extreme phenotypes favoured, intermediate phenotypes selected against, average indvs have lower fitness than extreme indv, bimodal distribution, fitness and upside down curve, graph more leveled and two peaks at ex terms
How does disruptive selection work in medium ground finches?
^beak size great for small seeds, smaller greater for large seeds, intermediate not bad for either but not good for either enough to competing saints extremes so it’s selected against, graph diaphragm shaped for fitness vs beak
What’s frequency dependent selection?
Fitness of each phenotype depends on how common or rare that phenotype is in pop, upside or right side dome, switches, can favour extremes or intermediate
How are male common side-blotched lizards an example of frequency depended selection?
Makes one in three different genetically based color morphs, each colour morph has different mating statergy, no single strategy best, rock paper scissors, yellow-not territorial and sneaky go into other territory’s and steal mates (beats orange), orange lots of wives, aggressive large territory and can usurp territory from blue mate guard era, blue monogamous and guards one female, beats sneaky yellow bc under scrutiny. Increasing one decrease another increases another which decreases oh and the cycle repeats
When is natural selection more powerful?
In larger populations, can lead to large changes over time only based on fitness, no luck bc genetic drift can get rid of traits that increase fitness, n]bas luck and good luck even out in large populations
What is sexual selection?
Subcategory of natural selection, definition debated, og Darwin said sexual selection arises form variation in ability to acquire and fertilize mates, might favour different traits than natural selection selection, shuker and kvarnemo sexual selection is selection arising from non random chance in competition for gamete’s or fertilization
