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31 Cards in this Set
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3 factors affecting allele frequencies |
1. Natural selection 2. Genetic drift 3. Gene flow mutations are low and rare, random mating doesn’t have a big effect in the overall gene pool so little impact on evolution |
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Natural selection and allele frequency |
Selection results in alleles being passed to the next generation in proportions that differ from those in present generation Causes adaptive evolution Ex: DDT-resistant allele in fruit flies was 0% before 1930. DDT comes out and 30 years later, The allele was in 37% of the population |
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Adaptive evolution |
A process in which traits that enhance survival or reproduction increase over time Ex: DDT-resistant allele in fruit flies |
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Genetic drift |
How allele frequencies fluctuate in predictably from one generation to the next By chance Size of population matters. Smaller, greater chance will impact vs larger (coin flip example) Reduces genetic variation through losses of alleles 2 types: founder effect and bottle neck effect |
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Founder effect |
Few individuals become isolated from larger population and start a new population Allele frequencies in the small founder population can be different from those in the other population Ex: Maple syrup urine disease: having extra finger or toes often occur more in the Amish population Ex: island that has increase in blindness due to be inhabited by a small group (someone had this allele and the gene pool is smaller) |
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Bottleneck effect |
Occurs if there is a dramatic reduction in population size due to a sudden change in environment The resulting gene pool may no longer be like the original population gene pool If remains small may be further affected by genetic drift |
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Genetic drift summary |
1. More significant in smaller populations 2. Can cause allele frequencies to change at random 3. Can lead to loss of genetic variation within populations 4. Can cause harmful alleles to become fixed |
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Gene flow |
Movement of alleles among populations Alleles can be transferred through movement of fertile individuals or gametes (pollen) Reduce variation among populations over time Ex: if it happened a lot among humans we would all blend together |
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Gene flow can affect adaptation to local environments |
Snakes on mainland with bands and snakes on island with no bands which makes them safe No natural selection bc mainland snakes keep going to island and adding band-genes in the population |
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Gene flow can increase or decrease fitness of a population |
Consider the spread of alleles for resistance to insecticide in mosquitoes Gene flow is an important agent of evolutionary change in modern human populations |
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Only mechanism that consistently causes adaptive evolution |
Natural selection Through sorting alleles that are favored and by chance Only natural selection can increase the frequencies of alleles that provide reproduction Acts on an organisms phenotype |
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Relative fitness |
Contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals (more kids, more success) Phrases imply competition among individuals. Reproductive success is more subtle |
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3 modes of selection |
1. Directional 2. Disruptive 3. Stabilizing |
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Directional selection |
Favor individuals at one extreme end of phenotype range |
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Disruptive selection |
Favors individuals at both extremes of phenotypic range Dark and light mice match dark and light rocks |
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Stabilizing selection |
Favors intermediate variants and acts against extreme phenotypes |
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Three selections |
A |
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Adaptive evolution |
Occurs at the degree to which a species is well suited for life for life in its environment improves Because the environment can change, continued process |
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Does not consistently increase the frequency of alleles that enhance survival and reproduction |
Genetic drift and gene flow |
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Increases frequency of alleles that enhance survival and reproduction |
Natural selection Genetic drift and gene flow can increase or decrease |
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Sexual selection |
A process in which individuals with a certain inherited characteristics are more likely to acquire mates than other individuals of the same sex |
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Sexual dimorphism |
Marked differences btw the sexes in secondary sexual characteristics (aka sexes look difference) IE: peacocks: male is colorful, female is brown |
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Intrasexual selection |
Direct competition among individuals of one sex for mates (often males) Deers, monkeys |
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Intersexual selection |
Mate choice usually in females who are choosy. (Showiness like with the peacocks) |
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Good genes hypothesis |
Ie: In frogs, Females like a long call. Does it mean better genes? Took short call frogs and long call frogs sperm and IVFd it with eggs. Long call progeny had better survival, larvae growth, and matured faster |
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Balancing selection |
When natural selection maintains stable frequencies of two or more phenotypic forms in a population 2 types: frequency-dependent and heterozygote advantage |
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Frequency-dependent |
Fitness of phenotype depends on how common it is in the population Ie: equal numbers of fish are born right mouthed or left mouthed. Eat scales. Population of left mouth increases, fish learn to guard themselves on that side. So then right mouths increase. |
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Heterozygote advantage |
Heterozygote genotype has higher fitness than both homozygotes Ie: sickle cell. People who are Aa have ability to fight off malaria but aa will make you sick and AA will not fight off malaria |
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Natural selection cannot fashion perfect organisms |
1. Selection can act only on existing variations 2. Evolution is limited (arms becomes wings) 3. Adaptations are often compromises (human shoulder is flexible but vulnerable to injury and if we wanted to boost structure, we would have less flexibility) 4. Chance natural selection and the environment interact |
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List of what humans deal with |
Compromises. Need each of these. Child birth pain: we are upright and so we have a smaller pelvis holes and grew brains Anxiety disorders: we needed to be alert, fight, flight or freeze |
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Evolutionary reasons we are vulnerable to disease |
See pic |
