20.5 Evolution Flashcards
what is the gene pool?
sum total of all the genes in a population
what is the allele frequency?
the relative frequency of a particular allele in a population
what is evolution?
the change in allele frequencies in a population over time
what is p in p+q = 1
the frequency of the dominant allele
what is q in p+q = 1
the frequency of the recessive allele
what are the conditions of the Hardy-Weinberg Principle?
- there are no mutations
- there is no emigration/immigration
- there is no selection
- mating is random
- the population is large
why is the Hardy-Weinberg Principle flawed?
it is very unlikely for a population to meet all of its conditions
THEREFORE
its is theoretical NOT realistic
what is p2 in
p2 + 2pq + q2 = 1
frequency of homozygous dominant genotype in a population
what is q2 in
p2 + 2pq + q2 = 1
frequency of homozygous recessive genotype in a population
what is 2pq in
p2 + 2pq + q2 = 1
frequency of heterozygous genotype in a population
what factors lead to changes in the allele frequency within a population?
mutations
sexual selection
gene flow
genetic drift
natural selection
how do mutations change the allele frequency?
they are the reason for new alleles being produced which leads to genetic variation
how does gene flow change the allele frequency?
emigration/immigration leads to changes in the allele frequency with populations increasing
how does genetic drift change the allele frequency?
a new allele will have a greater impact on a smaller population than a larger population as there are fewer alleles in the gene pool
what is genetic drift?
the change in allele frequency due to random chance
how does natural selection change the allele frequency?
increases the number of organisms with the survival characteristics which, after reproduction, leads to an increase in allele frequency
what is the genetic bottleneck effect?
when a population is greatly reduced in size which limits its genetic diversity
how did elephant seals suffer from the bottleneck effect?
they were heavily hunted in the 1800s
eventually population was only 20
now have a larger population of 30,000
BUT
now have a lower genetic diversity as the gene pool has been massively reduced so needs many generations to recover
what is the founder effect?
when a smaller population, which has a much smaller gene pool, is at greater risk to rare alleles which are now more frequent due to a lack of genetic variation
how did the Amish people suffer from the founder effect?
Amish people had a small closed community who mainly interbred
this led to a small gene pool where there was a higher frequency of rare genetic diseases
what are the 3 types of selection?
stabilising
directional
disruptive
what is stabilising selection?
the extremes are selected AGAINST
and the average is selected FOR
leads to increase in the average characteristic alleles
leads to reduction in the extreme characteristic alleles
what is an example of stabilising selection?
a baby’s weight:
- babies who are over or under weight (so an extreme) are less likely to survive
- babies who have an average weight are more likely to survive
what is directional selection?
one of the extremes is selected FOR
the other extreme is selected AGAINST
leads to increase in the allele frequency of one extreme
leads to reduction in the allele frequency of the other extreme
what is an example of directional selection?
moth colour:
- industrial revolution led to darkening which made light moths stand out
- this also camouflaged the black moths
- over time the white moths were eaten (one extreme against)
- and the black moths reproduced and survived (one extreme for)
what is disruptive selection?
both extremes are selected FOR
the average is selected AGAINST
leads to increase in the allele frequency of both extremes
leads to decrease in the allele frequency of the average
