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Mechanism of Evolution

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Biology 2483A
Hugh Henry

Mechanism of EvolutionPhenotypegenotype plus the environment driven by differences in allele frequencies Mutationsraw materials that fuel adaptationsfundamentallyrequire mutations to come up with different allelesthis is something that doesnt occur very often Not going to see very many changesonce in a whilehappens so infrequently we wont see short term changes Stabilizingfavoring ones in the middleFlies that inject larvaes in plant gullswasps select small gull sizes know theres a flywant to have their eggs grow on the larvae because they have trouble with the larger ones birds open the larger ones You can have some examples in the population where 1 allele that is favoured essentially becomes fixed Geese is an examplehappen to involve hemoglobin with high affinity for oxygenmassive advantage for survival and reproduction Very strong forceall or nothing Genetic drift is a random processmainly affects small populations 10 flowershalf are pink half are whitebranch falls and wipes out one phenotyperandom chance different when the population is larger Computer simulations looking at populationsrandom eliminations from a populationeach line is a simulationlooking at the pointssometime you lose it entirely or it becomes fixed at 100 Nothing is being favouredLarger populations are more towards the center The initial frequency of the A allele is 50 in all populations By generation 20 genetic drift has led to the fixation of the A allele in 7 populations and to its loss in 5 other populations Concept of genetic driftless variation in population Less Solution was to increase genetic variation by bringing in other organisms and get rid of harmful allelesBy 1993 the greater prairie chicken population in Illinois had dropped to fewer than 50 birds and was experiencing the negative effects of genetic drift on small populationsCenturies agomassive habitat over run with chickens and now barely anything In 1820 the prairies in which greater prairie chickens live covered most of Illinois In 1993 less than 1 of the original prairie habitat remained and the greater prairie chicken could be found in only 2 locations variation if you are losing alleles Chickens population was less than 50 because of land use changeconverted to farmlandlow genetic variation but this was manifest in terms of reproductionhalf of the eggssuggest that harmful alleles are getting fixed in the population and theres no selection to remove themTend to get differences in populationssee more variation in some and less in other
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