T7 Flashcards
fitness
a measure of their evolutionary success and their genetic contribution to the next generation
- eg producing lots of fertile offspring
this makes individuals best fitted for their environment
how does evolution by natural selection arise?
because individuals in a population differ in fitness
the fitter the individual for the environment, the more likely to survive and reproduce, passing on their alleles as opposed to others and changing the allele frequency
surivival and fitness
survival doesnt necessarily correlate to increased fitness, only if it plays a role in reproducing
- if increased survival allows for more offspring to be produced then it increases fitness
- but if increased survival does not cause more offspring to be produced then it doesn’t affect fitness
evolution requires genes so if they are not passed on, it is irrelevant how long you live
natural selection for a species
the traits are chosen for the individuals benefit, not the entire species
- it then becomes a benefit for the species in the long run but the selection of traits arent working together to prevent extinction, only what is beneficial at the time
- sometimes traits can be unsuccessful for the species
traits are only selected for…
increased or beneficial to reproductive success
genotypic fitness
this involves
- survival to adulthood
- offspring produced
the genotype may be the same but the expression and fitness may differ
relative fitness
the absolute fitness of each genotype divided by the absolute fitness of the fittest genotype in a population
- looks at the reproductive rate and then can compare these relative fitnesses to see what trait is most fit
spread of a trait in a population
need to look at the absolute fitness of each genotype
- if a high absolute fitness, it will spread quicker as most fit, highest reproductive rate
coffeicent of selection
1-relative freq = s
this is a measurement of how much natural selection will attempt to reduce the relative contribution of a genotype to the next generation
0-1
0 = natural selection wont reduce, trait will pass on
1= natural selection very likely to reduce and trait wont pass on
graphs looking at the spread of frequency of alleles over time - this is for the simple single genetic traits
if a steep slope
- spread is quite fast
- normally dominant
if the difference in fitness is larger than the fitness difference is larger so the spread is quicker
for recessive allele is fit that still can spread
- the slope would be very linear for a while and then increase exponentially because
- the frequency of a recessive allele is higher in heterozygotes rather than homozygotes so. the phenotype wouldn’t be displaying the recessive allele
- so takes time
for continuous traits and their evolution - polygenic traits
using a bar graph to look at the trait and the number of individuals with that trait
then produce a fitness profile
- shows the relationship between the fitness of the trait and the number of individuals
eg if had body size as our trait, the fitness profile shows that as body size increases, fitness increases
- so individuals with an above average body size are fitter, so selection towards bigger body size
directional selection
positive or negative gradient fitness profile
- selection directional to one extreme phenotype
- common in areas where environments change
- phenotype changes towards the selection it is going to
stabilising selection
fitness profile showing a triangle, highest fitness in the middle, average phenotype
- most of the time, with stabilising selection, their isn’t always a change to the population trait
- this is normally when the environment tends not to change
disruptive selection
fitness profile = inverted triangle with highest fitness at either end of the extreme phenotypes, not the mean
- selecting for 2 different traits in same environment, this leads to speciation
- diverging population
fitness profile gradient
the steeper the profile, the quicker the evolution and stronger the selection
