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25 Cards in this Set
- Front
- Back
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microevolution |
change in allelic frequencies in a population over generations |
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causes of microevolution |
natural selection genetic drift gene flow |
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genetic drift |
chance events that alter allele frequencies (especially in small populations) can lead to a loss of genetic variation can cause harmful alleles to become fixed |
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founder effect |
cause of genetic drift few members from a larger population establish a new population |
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bottleneck effect |
a sudden change in the environment drastically reduces the size of a population |
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gene flow |
transfer of alleles between populations reduces variation in populations over time increases fitness of a population |
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cause of microevolution that causes adaptive evolution |
natural selection |
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hardy weinberg equilibrium |
no mutations random mating no natural selection large population size no gene flow equations p + q = 1 p^2 + 2pq + q^2 = 1 p = dominant allele frequency q = recessive allele frequency |
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sources of genetic variation |
formation of new alleles altering gene number or positions rapid reproduction sexual reproduction |
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formation of new alleles |
mutations gametes point mutations: can be harmless or neutral because of redundancy in genetic code ---> can be harmful if change in protein production ---> sometimes beneficial |
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mutation rates |
low in animals and plants lower in prokaryotes higher in viruses |
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sexual reproduction |
genetic variation through crossing over independent assortment of chromosomes fertilization |
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relative fitness |
the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals acts on phenotype, resulting in indirectly acting on genotype |
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directional selection |
when conditions favor individuals exhibiting one extreme of a phenotypic range common when a population's environment changes |
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disruptive selection |
when conditions favor individuals at both extremes of a phenotypic range over intermediate |
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stabilizing selection |
conditions favor individuals in an intermediate phenotype reduces variation and tends to maintain a status quo |
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sexual selection |
form of natural selection in which individuals with certain characteristics are more likely to obtain mates |
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sexual dimorphism |
difference in secondary sexual characteristics between male and females of the same species (eg. peacocks) |
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intrasexual selection |
selection within the same sex individuals of one sex compete directly for mates eg. patrolling, competition |
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intersexual selection |
mate choice individuals of one sex are choosy in selecting mates from the other sex |
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diploidy |
maintains genetic variation in the form of hidden recessive alleles heterozygotes sneak by hiding from selection |
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balancing selection |
when a population maintains stable frequencies of phenotypes |
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heterozygote advantage |
when heterozygotes have a higher fitness than homozygotes eg. sickle cell |
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frequency dependent selection |
the fitness of a phenotype depending on how common it is in a population eg. scale eating fish with left and right mouths |
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why perfect organisms dont exist |
selection can only act on existing variations (advantageous alleles do not arrive on demand) evolution is limited by historical constraints (cannot scrap ancestral anatomy) adaptations are often compromises chance, natural selection, and the environment interact |
