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Biology 102 > Lecture Notes: Population Genetics > Flashcards

Lecture Notes: Population Genetics Flashcards

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1
Q

population genetics overview

A

studies the variation in gene/allele frequencies through time

1940’s Integration of evolutionary theory with genetics; neodarwinism (modern synthesis)

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2
Q

neodarwinism

A

population are the units of evolutions, not individuals
natural selection is the most important mechanism, but there are others
gradualism

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3
Q

population

A

localized group of interbreeding individuals of the same species

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4
Q

Gene Pool

A

total set of genes in a population

fixed alleles: those for which all of the individuals in a population are homozygous

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5
Q

Hardy Weinberg Model

A
  • gene pool in equilibrium
  • meiosis and random fertilization maintain the same allele/genotype frequency as in P1, then the population is equilibrium
  • if values start to deviate, then the population is evolving
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6
Q

Hardy Weinberg Assumptions

A
  1. Large population size
  2. no random genetic drift
  3. no gene flow
  4. no mutation
  5. panmixia ( complete random mating)
  6. No natural selections
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7
Q

microevolution

A

change in genotype/allele frequencies in a population from generation to generation

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8
Q

Mechanisms of evolultion

A
  1. random genetic drift
  2. gene flow
  3. mutation
  4. non-random mating (inbreeding and assortative mating)
  5. Natural Selection
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9
Q

Random Genetic Drift

A
  • changes in the gene pool of a small population due to chance
  • sampling error: disproportionate results in small samples
  • new generations get alleles at random so:
    a. the smaller population size, the greater the chance that the allele frequencies in the new generation will not represent P1
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10
Q

Conclusion of random genetic drift

A

the changes in frequencies from one generation to the next is unpredictable (random sampling of alleles)

on average small populations will have some alleles fixed faster than larger populations

leads to two phenomena: bottleneck and flounder

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11
Q

bottleneck effect

A
  • a drastic environmental change can results in small sample of population surviving
  • the smaller the sample, the less the chance that its gene pool is representative of the original population
  • leads to the decreased variation
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12
Q

founder effect

A
  1. few colonizing individuals that survive
  2. sample unlikely to be representative of population of origin
  3. specially important in islands
  4. wallace line
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13
Q

gene flow

A
  • genetic exchange by migration of fertile individuals or exchange of gametes between populations
  • directions and flow affects the change in the gene pool
  • if rates of flow are equal, gene flow has a homogenizing effect among divergent population
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14
Q

Mutations

A
  • basic origin of variation
  • if it occurs in gametes, then it is transmitted to the next generation, and affects the gene pool
  • rates vary among groups and gene loci
  • small effects in large populations
  • rate of spread of mutations can increase by the disproportionate reproduction of some populations
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15
Q

non-random mating

A

can occur by:

a. inbreeding: mating among close relatives or self-fertilization
b. assortative mating: selection of mates based on specific phenotypes
- leads to loss of variation
- specially important in sessile organisms

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16
Q

Natural Selection

A
  • Differential reproductive success based on the variation among individuals within a population
  • leads to adaptation: accumulation and maintenance of more favorable genotypes for a specific enviornment
17
Q

Mode of natural selection

A
  • stabilizing
  • directional
  • diversifying (disruptive)
18
Q

Stabalizing Selection

A
  • selection against extreme phenotypes
  • selection for average phenotypes
  • results in reduced variation
19
Q

Directional Selection

A
  • Selection against one extreme
  • opposite extreme phenotype is favored
  • results in shift in average phenotype

ex: increase horns in cattle to protect the calfs

20
Q

Disruptive Selection

A
  • selection against average phenotypes
  • extreme phenotypes are favored
  • results in bimodal distribution
21
Q

Variation

A
  • continuous: height
  • discrete : ABO blood groups
  • polymorphism: when 2 or more “morphs” of a discrete character are present in a population
22
Q

Clines

A
  • Gradual changes in a character along a geographical axis
  • interbreeding populations line up along the axis
  • environmental variables change gradually along the axis
  • some times the population at the extremes are reproductively isolated from each other, although there is a continuous gene flow along the axis
23
Q

origin of variation

A 
mutation
recombination
important aspect to remember:
a. generation time
b. neutralist vs selectionist
c. macromutation- "hopeful monster" vs homeotic genes
24
Q

Maintenance of variation

A

diploidy

balanced polymorphism

25
Q

diploidy

A

hiding the variation in heterozygote

a. the rarer the recessive allele is the greater the proportion in heterozygotes

26
Q

balanced polymorphism

A

NS maintains it in a population

27
Q

Examples of balanced polymorphism

A

a. heterozygote advantage
b. Hybrid Vigor
c. patchy environment + Natural Selection
d. frequency-dependent selection

28
Q

heterozygote advantage

A

heterozygotes with greater survivorship and reproductive success than homozygotes

ex: sickle cell anemia in areas with malaria

29
Q

Hybrid Vigor

A

crossbreeding between inbred varieties

leads to increased heterozygosity at many loci and decrease of deleterious recessives

30
Q

patchy environment + natural selection

A

heterogeneous environment within the boundaries of a population leads to maintenance of different phenotypes

31
Q

frequency-dependent selection

A

reproductive success of phenotype decreases if the density of the phenotype increases

Biology 102 (16 decks)

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