Hardy-Weinberg Principle

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Hardy-Weinberg Principle. Hardy-Weinberg - original proportions of genotypes in a population will remain constant from generation to generation Sexual reproduction (meiosis and fertilization) alone will not change allelic (genotypic) proportions. Hardy-Weinberg Equilibrium. - PowerPoint PPT Presentation

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PowerPoint Presentation*
bb = white
B_ = black
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population size is very large
random mating
no mutation
no selection occurring
(p+q)2 = p2 + 2pq + q2
p2 = individuals homozygous for first allele
2pq = individuals heterozygous for alleles
q2 = individuals homozygous for second allele
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16 cats white = 16bb then (q2 = 0.16)
This we know we can see and count!!!!!
If p + q = 1 then we can calculate p from q2
Q = square root of q2 = q √.16 q=0.4
p + q = 1 then p = .6 (.6 +.4 = 1)
P2 = .36
All we need now are those that are heterozygous (2pq) (2 x .6 x .4)=0.48
.36 + .48 + .16
Mutation
Mutation rates are generally so low they have little effect on Hardy-Weinberg proportions of common alleles.
ultimate source of genetic variation
Gene flow
tend to homogenize allele frequencies
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Nonrandom mating
assortative mating - phenotypically similar individuals mate
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Genetic drift – statistical accidents.
important in small populations
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Selection – Only agent that produces adaptive
evolutionary change
variation must exist among individuals
variation must result in differences in numbers of viable offspring produced
variation must be genetically inherited
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Selection pressures:
avoiding predators
Measuring Fitness
Fitness is defined by evolutionary biologists as the number of surviving offspring left in the next generation.
relative measure
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Interactions Among Evolutionary Forces
Levels of variation retained in a population may be determined by the relative strength of different evolutionary processes.
Gene flow versus natural selection
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Frequency-dependent selection
Negative frequency-dependent selection favors rare phenotypes.
Positive frequency-dependent selection eliminates variation.
Oscillating selection
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Sickle cell anemia
Homozygotes exhibit severe anemia, have abnormal blood cells, and usually die before reproductive age.
Heterozygotes are less susceptible to malaria.
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Stabilizing selection
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Selection on Color in Guppies
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Selection on Color in Guppies
High predation environment - Males exhibit drab coloration and tend to be relatively small and reproduce at a younger age.
Low predation environment - Males display bright coloration, a larger number of spots, and tend to be more successful at defending territories.
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Evolution requires genetic variation
Intense selection may remove variation from a population at a rate greater than mutation can replenish.
thoroughbred horses
epistatic interactions