Evolution change in allele frequencies

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Evolution change in allele frequencies
within populations
Population genetics study of genetic
structure of populations
allele frequencies
genotype frequencies
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Population genetics

• genotype frequencies
• allele frequencies

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Describing genetic structure

• calculations
• collecting data
• patterns of genetic variation

What can cause changes in allele frequency?

• Hardy-Weinberg equilibrium
• non-equilibrium conditions

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Allele and genotype frequencies
allele frequencies
genotype frequencies
200 white (rr) 500 pink (Rr)
300 red (RR)
200/1000 0.2 rr 500/1000 0.5 Rr 300/1000
0.3 RR
900/2000 0.45 r 1100/2000 0.55 R
total 1000 flowers
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for a populationwith genotypes
calculate
Genotype frequencies Phenotype
frequencies Allele frequencies
100/400 0.25 GG 160/400 0.40 Gg 140/400
0.35 gg
100 GG 160 Gg 140 gg
260/400 0.65 green 140/400 0.35 brown
360/800 0.45 G 440/800 0.55 g
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another way to calculateallele frequencies
Genotype frequencies Allele frequencies
0.25 GG 0.40 Gg 0.35 gg
0.25
100 GG 160 Gg 140 gg
0.40/2 0.20
0.40/2 0.20
0.35
360/800 0.45 G 440/800 0.55 g
OR 0.25 (0.40)/2 0.45 0.35
(0.40)/2 0.65
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How can we get information about genotypes and
alleles in populations?

• observe phenotypes
• protein data (electrophoresis)
• DNA data (electrophoresis or sequencing)

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How can we get information about genotypes and
alleles in populations?

• observe phenotypes
• protein data (electrophoresis)
• DNA data (electrophoresis or sequencing)

Polymorphism more than one allele at a locus
How common is polymorphism?
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How genetically variable are populations?
H0 little variation
- because selection should remove less fit
alleles - implies mutations either good or bad,
not neutral
Ha lots of variation
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Allele frequency variationwithin and between
populations
Frequency of Mdh-1 alleles in snail colonies in
two city blocks
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Allele frequency variation in time
Changes in frequency of allele F at the Lap
locus in prairie vole populations over 20
generations
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How genetically variable are populations?
H0 little variation
- because selection should remove less fit
alleles - implies mutations either good or bad,
not neutral
Ha lots of variation
neutral theory most mutations are neutral
selectionist theory variation in selection
maintains different alleles in population
- heterozygote advantage - fluctuating selection
(selection varies in time or space) -
frequency-dependent selection (rare allele is
advantageous)
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Population genetics

• genotype frequencies
• allele frequencies

?
Describing genetic structure

• calculations
• collecting data
• patterns of genetic variation

?
What can cause changes in allele frequency?

• Hardy-Weinberg equilibrium
• non-equilibrium conditions