Evolution

What is a gene pool?
The sum total of all the genes in a population at a given time
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What is allele frequency?
The relative frequency of a certain allele in a population
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What affects the frequency of a gene?
Environmental factors- changing conditions and natural selection, doesnt matter if the allele is dominant or recessive
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In a diploid breeding population with 2 potential alleles (dom and recess), the frequency of the dominant plus the frequency of the recessive will always equal what?
1 (p+q=1)
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What does the Hardy-Weinberg principle state?
In a stable population with no disturbing factors, the allele frequency will remain the same from one generation to the next and no evolution will occur
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What do we use the Hardy-Weinberg principle for?
To measure and study evolutionary changes within a population
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Name a problem with the Hardy-Weinberg principle
It assumes a theoretical breeding population of diploid organisms that is large and isolated, also that has no mutations and selection pressures, this is virtually impossible as species are continually changing due to the environment etc
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Name a few factors that affect evolution
Mutation, Sexual selection (increased no. alleles that increase mating success) Gene flow (movement of alleles in a population due to immigration etc) Genetic drift (change in allele frequency due to random nature of mutation), Natural selection
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Why are large populations advantageous?
They have lots of genetic diversity meaning selection pressures dont wipe out the entire population as there are extremes that will survive
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Name 2 types of limiting factors for population size
Density-dependent and density-independent
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What are density-dependent factors?
Limiting factors which are dependent of population size, e.g. competition, communicable diseases, predation
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What are density-independent factors?
Limiting factors which dont depend on population size and affects all populations in the same way, e.g. climate change, natural disasters, deforestation
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What is a population bottleneck?
When an event occurs which greatly reduces the population, reducing the gene pool greatly, then we have the founder effect as the population grows again
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What is the founder effect?
When samples of a population establish new colonies, this can occur due to a natural disaster etc, and they become smaller populations with very different smaller gene pools
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Give an example of a population bottleneck
Northern elephant seals were hunted down to about 20 seals, the hunting of them was band and the population grew again (30,000) however the new population was a lot less genetically diverse
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What is a positive that can occur through a population bottleneck?
A beneficial gene can have a greater impact on a population and lead to a quicker development of a new species
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Give an example of the founder effect
Amish have little genetic variation as they are a closed community, 2 founders had ellis-van creveld disease, the allele that caused that grew in frequency due to small gene pool, amish have unusual high frequencies of this disorder
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What is normal distribution?
The distribution of variants within a population forming an equal bell curve
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What is stabilising selection?
A form of natural selection which maintains the bell curve normal distribution, extremes dont tend to survive and the average is the most common which do survive due to the characteristic being advantageous
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What is positive selection?
A phenotype being selected for, in stabilising selection this is the norm/ average value
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What is negative selection?
A phenotype being selected against, in stabilising selection it is extreme values
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What is directional selection?
When the norm/ average phenotype isnt the most advantageous anymore due to a change in the environment
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Give an example of directional selection
Peppered moths used to be light coloured to blend in with the bark, however the industrial revolution caused bark to be darker so the darker peppered moths, which used to be more visible and so more predated are now more advantageous and disguised
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What is disruptive selection?
The opposite to stabilising selection, where the norm is negatively selected and the extremes are positively selected, it is rare but can still happen
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Other cards in this set

Card 2

Front

What is allele frequency?

Back

The relative frequency of a certain allele in a population

Card 3

Front

What affects the frequency of a gene?

Back

Preview of the front of card 3

Card 4

Front

In a diploid breeding population with 2 potential alleles (dom and recess), the frequency of the dominant plus the frequency of the recessive will always equal what?

Back

Preview of the front of card 4

Card 5

Front

What does the Hardy-Weinberg principle state?

Back

Preview of the front of card 5
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