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Miderm p2 eemb22

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eshapeesha's version from 2017-05-05 09:16

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Question Answer
Outline and discuss the basic steps of the evolutionary process.variation, natural selection, genetic divergence, reproductive isolation, speculation.
a) sources and types of variationnormal variation. this is quantitative and continuous (height, weight); polymorphic variation which is discreet (eye color, blood groups), ecogeographic variation- variation along a ecological or geographic gradient. can occur as a cline (bird wing length)
b) types of natural selection1)stabilizing selection- individuals that are well adapted cluster around the mean (human birth weight), 2) directional selection- favors survival and reproduction of phenotypes at one extreme or the other of phenotypic distribution. individuals that deviate from the avergae are favored. occur when mutations appear and prove adaptive. (peppered moth) 3) disruptive selection- phenotypic characters at opposite extrmes of character distribution are favored and intermediate forms are selected against. this occurs in diverse and shifting environments (ex- black bellief seedcracker finches need to have big or small beaks for large or soft seeds. if in between they cant eat)
artificial selectionselection and breeding of individuals with desired traits by humans
prezygotic isolation1)ecological isolation (ex- california oaks), 2)geographic isolation (ex- head lice, body lice so geographic isolation is the hariless region of the neck), 3)temporal isolation- isolated by reproductive events that occur at different times (ex- cicadas where some reproduce every 17 years and the sibling species does every 13 years and every 221 years these happen at the same time); 4)ethological isolation (ex- birds where females recognize behavioral signals by males), 5) mechanical isolation 6) gametic isolation- gametes of different species are incompatible at the molecular level resulting in mortality
postzygotic isolationafter fertilization. 1) zygotic wastage- minimum number of zygotes required per species to achieve a viable adult. 2) hybrid sterility- no viable sperm or egg. 3) hybrid inviability- egg of one species is fertilized by sperm from another species, but fertilize egg cannot develop past early embryonic stages. 4) hybrid breakdown- offpsring fertile but their offpsring are sterile or have genetic abnormalities.
e) speciationchanges in allele frequencies that are significant enough to mark the formation of daughter species from parent species.
biological species concept1)species are groups of interbreeding natural populations that are reproductively isolated from other such groups 2) the capacity to contribute to a shared gene pool is qualification for species membership. 3) this concept does not apply to asexually reproducing organisms.
mechanisms of speciation1)allopatric speciation- physical barriers lead to reproductive isolation. 2) sympatric speciation- a species may form within the home range of an existing species in the absence of physical barriers. this includes polyploidy- during cell division an accident can result in an extra set of chromosomes. and parapatry- adaptation to local environments and sexual selection promote speciation.
Describe and provide examples of the bottleneck effect and the founder’s effectbottleneck effect- severe reduction in population size bc intense selection pressure or natural disaster. founders effect- when a few individuals become isolated from a larger population. occurs when a few members migrate to a new habitat. isolated gene pool may no longer represent the original population. in the absense of gene flow, ntural selection will alter allelic frequencies in different ways due to genetic drift (isolated islands)
Define mass extinctionsimultaneous loss of many lineages from earth. Identify the number of recorded mass extinction events throughout the history of life on earth? 5
Describe the primary causes of mass extinction events.catastrophic methane release, flood basalt eruptions (large scale volcanic activity), climate change, impact events
Describe the two theories that have been postulated to explain the mass extinction event at the K-T boundary that eliminated the dinosaurs.1) a gigantic impact crater 170 miles across and 1 km deep landed on earth off the coast of the yucatan peninsula. the asteroid that hit here had to be 12 miles wide. couldn've also been a huge volcanic eruption called the deccan eruptions (actually lava flows) which began right before the kt boundary. peak eruptions may have only lasted 1 million years
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