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change in the genetic makeup of a population from generation to generation
example: drug resistance bacteria (penicillin), strands of HIV resistive to drugs
evolutionary change on its smallest scale |
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| the study of how populations change genetically over time |
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| a comprehensive theory of evolution that integrates ideas from many other fields |
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| a localized group of individuals that are capable of interbreeding and producing fertile offspring |
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the aggregate of genes in a population at any one time
- consists of all alleles at all gene loci in all individuals in a population |
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| - the frequencies of alleles and genotypes in a population's gene pool remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work |
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| Hardy-Weinberg Equilibrium |
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Definition
- the population will have the same allele frequencies from one generation to the next AND its genotype frequencies can be predicted from the allele frequencies
**assumes that individuals in a population donate gametes to the next generation at random AND mate at random |
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| Calculating genotype frequencies in the next generation according to HWP |
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Definition
( p + q ) X ( p + q ) = p^2 + 2pq + q^2
where p is the frequency of allele #1 and q is the frequency of allele #2 |
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| Conditions for Hardy-Weinberg Equilibrium |
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Definition
1. Extremely Large Population Size
2. No Gene Flow
3. No mutations
4. Random Mating
5. No Natural Selection
** these conditions are rarely met
** departure from these conditions results in evolution |
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Definition
- changes in the nucleotide sequence of DNA
- weak evolutionary force |
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- a change in one base in a gene
- mostly harmless
- example of significant impact: sickle-cell disease |
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| Insertion/Deletion mutation |
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Definition
"Indels" can cause frameshift mutations or add/subtract amino acids
- almost certain to be harmful |
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- duplication of a short stretch of DNA
- caused by unequal crossovers during meiosis
- may maintain function, gain a new function, or lose function
*nearly always harmful |
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Definition
Part of a chromosome breaks in two places, flips, and the reanneals
- ABCDEF -> ABEDCF |
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The condition whereby an organism has 2 or more sets of chromosomes, usually resulting in a failure of reduction division
- may cause instant speciation |
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- reshuffling of the existing alleles in a gene pool
- caused by random assortment of chromosomes and crossing over within chromosomes |
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| Three Major Factors That Cause Most Evolutionary Change: |
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Definition
1. Natural Selection
2. Genetic Drift
3. Gene Flow |
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Definition
Unpredictable fluctuations in allele frequencies from one generation to the next because of a population's finite size
Over time drift tends to reduce genetic variation through losses of alleles from the gene pool |
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| 2 Major Examples of Genetic Drift |
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Definition
1. bottleneck effect
2. founder effect |
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Definition
A sudden catastrophe drastically reducesthe size of the population and the surviving gene pool is no longer reflective of the original population's gene pool
- by chance, some alleles are over represented, some are under represented, and some are eliminated
example: 1890 hunting of northern elephant seals in CA reduced the population to 20 individuals ... although pop. size is now ~ 30,000 all have the same genes |
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- When a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pool is not reflective of the source population
*think: white guys on a boat at Plymouth rock produce a bunch of white guys |
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- genetic additions to and/or subtractions from a population resulting from the movement of fertile individuals or gametes
- causes a population to gain or lose alleles
- tends to reduce differences between populations over time
** think about humans moving much more freely about the world that in the past ** |
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Definition
| if two or more distinct "morphs" are each represented in high enough frequencies to be readily noticeable |
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- not distinct and separate morphs, but a continuum
example: heights of humans varies along a continuum |
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differences between the gene pools of separate populations
example: house mice separated by mountains on an island will evolve in isolation from one another |
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| the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals |
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| the contribution of a genotype to the next generation compared to the contributions of alternative genotypes for the same locus |
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Definition
1. Directional Selection
2. Disruptive Selection
3. Stabilizing Selection |
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Definition
- shifts the frequency curve for some phenotypic character in one direction or the other by favoring individuals that deviate from the average
- most common when a population's environment changes or when members of a population migrate to a new habitat with different environmental conditions than the former one
example: moth colors and the industrial revolution |
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- occurs when conditions favor individuals on BOTH extremes of a phenotypic range over individuals with intermediate phenotypes
- birds who live on soft seeds and hard seeds need either a small bill or a large-bill but a medium bill is useless |
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- acts against extreme phenotypes and favors intermediate variants
- reduces variation and maintains the status quo for a particular phenotypic character
example: human babies lie in the range of 3-4 kg; babies who are much smaller or larger suffer higher rates of mortality |
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| Reasons for the preservation of genetic variation (3) |
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Definition
1. Diploidy
2. Balancing Selection
3. Heterozygote Advantage |
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Term
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Definition
- genetic variation is hidden from selection in the form of recessive alleles
- recessive alleles survive in heterozygous carriers
example: cystic fibrosis is maintained in the population even though it sucks |
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Definition
- occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population
- leads to balanced polymorphism
- includes heterozygote advantage and frequency-dependent selection |
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Definition
if individuals who are heterozygous at a particular gene locus have greater fitness than the homozygotes, natural selection will tend to maintain two more alleles at that locus
example: in Africa, the heterozygotes are resistant to malaria even though dominant individuals are much more susceptible to the disease while recessive individuals develop sickle-cell anemia |
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Term
| Frequency-Dependent Selection |
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Definition
| - the fitness of any one morph declines if it becomes too common in the population |
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Definition
- natural selection for mating success
examples: select for size, color, and ornamentation |
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| - marked differences between the sexes in secondary sexual characteristics which are not directly associated with reproductions |
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| Why Natural Selection Cannot Fashion Perfect Organisms: (4) |
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Definition
1. Evolution is limited by historical constraints
2. Adaptations are often compromises
3. Chance and natural selection interact
4. Selection can edit only existing variations |
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Definition
- a certain genotype gets passed on
- when the allele frequency hits either 1 or 0 |
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