The change in allele frequencies in populations due to chance not selection Can include the loss of alleles from the gene pool Genetic drift The change in allele frequencies in populations due to ID: 797748
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Slide1
Genetic drift
Slide2Genetic drift
The change in allele frequencies in populations due to
chance
(not selection).
Can include the loss of alleles from the gene pool.
Slide3Genetic drift
The change in allele frequencies in populations due to
chance
(not selection).
Can include the loss of alleles from the gene pool.
Most likely to have an effect in small populations.
Slide4Genetic drift
The change in allele frequencies in populations due to
chance
(not selection).
Can include the loss of alleles from the gene pool.
Most likely to have an effect in small populations.
When populations are small it is likely that allele frequencies will change from generation to generation by chance and so drift into an increase or decrease (or complete loss). This has nothing to do with natural selection.
Slide5Eg of genetic drift
Consider a population of one couple – both are Bb (heterozygous for brown eyes)
B b
B BB Bb
b Bb bb
They have 2 children. The chances of one child being BB is ¼
The chances of both children being BB is ¼ x ¼ = 1/16
Slide6Eg of genetic drift
Consider a population of one couple – both are Bb (heterozygous for brown eyes)
B b
B BB Bb
b Bb bb
They have 2 children. The chances of one child being BB is ¼
The chances of both children being BB is ¼ x ¼ = 1/16
There is 1/16 probability of losing the b allele. The more children produced, the lower the chance of losing the b allele.
Slide7Eg of genetic drift
Consider a population of one couple – both are Bb (heterozygous for brown eyes)
B b
B BB Bb
b Bb bb
They have 2 children. The chances of one child being BB is ¼
The chances of both children being BB is ¼ x ¼ = 1/16
There is 1/16 probability of losing the b allele. The more children produced, the lower the chance of losing the b allele.
The chance of losing an allele through genetic drift DECREASES as the population size INCREASES.
Slide8Founder effect
Refers to a small group that colonise a new isolated area such as an island.
Slide9Founder effect
Refers to a small group that colonise a new isolated area such as an island.
The range and frequency of alleles present in this small group is not representative of that of the original population.
Slide10Founder effect
Refers to a small group that colonise a new isolated area such as an island.
The range and frequency of alleles present in this small group is not representative of that of the original population.
Some alleles may not be present in the group, others will be less frequent/ more frequent than in the original population.
Slide11Founder effect
Refers to a small group that colonise a new isolated area such as an island.
The range and frequency of alleles present in this small group is not representative of that of the original population.
Some alleles may not be present in the group, others will be less frequent/ more frequent than in the original population.
EG – introduced species (
kune
kune
pigs) are unlikely to have the range of alleles that were present in the original populations. This means they can become quite different from original populations and their evolution can progress faster.
Slide12Bottleneck effect
Populations may be suddenly reduced in numbers – typically because of:
-
Slide13Bottleneck effect
Populations may be suddenly reduced in numbers – typically because of:
A catastrophic event (flood, fire, landslide, drought) – removes individuals regardless of their genetic makeup.
Slide14Bottleneck effect
Populations may be suddenly reduced in numbers – typically because of:
A catastrophic event (flood, fire, landslide, drought) – removes individuals regardless of their genetic makeup.
Human action (habitat destruction, or introducing predators) removing original individuals.
Slide15Bottleneck effect
Populations may be suddenly reduced in numbers – typically because of:
A catastrophic event (flood, fire, landslide, drought) – removes individuals regardless of their genetic makeup.
Human action (habitat destruction, or introducing predators) removing original individuals.
Because numbers fall rapidly, the
range of alleles decrease and the frequencies of alleles will change
Slide16Bottleneck effect
Populations may be suddenly reduced in numbers – typically because of:
A catastrophic event (flood, fire, landslide, drought) – removes individuals regardless of their genetic makeup.
Human action (habitat destruction, or introducing predators) removing original individuals.
Because numbers fall rapidly, the
range of alleles decrease and the frequencies of alleles will change
If the population increases again, it will have reduced genetic diversity.
EG – native
robins
https://
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KnpNKtmlxg