variation Flashcards
what was the first idea of how variation worked
blending
what is blending
trarits or bloods between paretsn blended leading to inheritance of acquired characteristics
this however removed variation giving the idea a major flaw
what did fisher say about variation
showes continuous variation could be down to the combined effct of several genes
what s recurrent mutations
some alleles in the pop exisit because of this
selection is against the variation so mutations creates rare allese and selection removes them
what does fast mutations lead to
more mutant alleles and there wil be stronger selection against them
reduces the number of mutant allesles
example of recurrent mutations
most rare genetic disorders
what is the heterzygote advantage
better to be Aa than AA or aa
why is there a heterozygote advantage
maintains variation at a locus because the allele becomes fitter as it gets rarer
eg. sickle cell anameia
examples of heteroxygote advantage
wolves in yelow stone:
black is dominant
being homozygus for this gives low survival
grey wolves however live longest
what is negaative frequency dependent selection?
rare alleles having the rarity value with heterozygote advantage
what is positive frequence dependent selection
more common alleles will win
this however removes variation
what is gene flow in terms of variation
gene flow between pops can maintain variation
two alleles well adapted to different environments
what can migration between two areas cause
creates variable populations called clines which are changes in allele freq over distance
what is fluctuating selection
maintains variation
favoured alleles in one generaton can be distorted or disfavoured in the net
if the direction of the selection changed it maintains variation
what od neutral and nearly neutral theorys look at
the idea that seection has nothing to do with it
it calculates how fast evolution happens if variation is neutral
evolution rates equals mutations rates and predicts a molecular clock
what did the neeurtral theoryes work out
how much variation youd expect to find in a population if variation is neutral and has no effect on fitness
it says that alleles are amde by mutations and defit to a frequency of 1 or 0
according to the neutral theorys how much variation is expected/
it depends on mutations rates and population sizes
the effective population size
new alleles come in as one is lost, either the new one and there is no net change or the old one is lost and ther is evolution
what type of hypothesis does the neutral theory give us
its mathematical and gives us a null hypothesis
how can we tell is eolvution is happening in a biologicl system?
compare what we see to what the neutral theory predicts
what is slow evolution relative to mutation rates called
sequence conservatiojn or purifiying selection
negative selection
inidicates the sequence is well adapted already
what does very fast evolution indicate
the sequence is currently adapting
called adaptive evolution or positive selection
