Module 6: Evolution Flashcards
State the definition of gene pool
all the number of alleles in a population
State the definition of allele frequency
how often an allele occurs in a population
Describe how evoultion by natrual selction takes place
- variation caused by mutation
- selection pressure (disease, predation, competition)
- some are better adapted than others
- ones with advantgous allele most lkley to surivve wheras the others may die
- survivours reproduce, so greater proportion of next gen can inherit advantgous allele
- allele frequency increases
What does stabalising selection mean
natural selection that keeps allele frequencies relatively constant over generations
characteristics are in the middle range
usually in a stable enviorement
What is directional selection
happens in a changing environment
individuals with alleles more to the extreme are more likely to survive
How would directional selection occur in an environment
selection pressure favours a particular phenotype
Individuals with the favoured phenotype will survive and are more likely to reproduce and pass on the advantageous alleles to their offspring
others will probably die
So over time and several generations the frequency of the advantageous allele increases
and frequency of other alleles decreases
What is genetic drift
it is when chance affects which individuals in a population survive instead of selection pressures
How does genetic drift occur
variation in alleles within population
by chance one genotype is passed on more compared to others
so allele frequency of that allele increases
if by chance the allele is passed on, then it can lead to evolution
What kind of population does genetic drift mainly occur in
smaller populations
What is genetic bottleneck?
it is when an event such as an earthquake causes a previously large population to decrease dramatically in size
this means that one allele will be more common
What is the founders effect
it is when a small number of individuals from a large population start a new population, this means there is a small number of alleles in the gene pool
therefore population is more likely to be influenced by genetic drift
How does founders affect occur
migration or geographical isolation
What is the equation for hardy Weinberg
p + q = 1
p2 + q2 + 2pq = 1
What does p mean in hardy Weinberg
dominant allele
What does q mean in hardy Weinberg
recessive allele
What does 2pq mean in hardy Weinberg
heterozygous alleles
What does hardy Weinberg’s principle state
if certain conditions are met then the allele frequencies of a gene within a population will not change from generation to generation
What are the conditions of the Hardy Weinberg principle
Organisms are diploid
Organisms reproduce by sexual reproduction only
There is no overlap between generations
Mating is random
The population is large
There is no migration, mutation or selection
Allele frequencies are equal in both sexes
Define speciation
evolution of a new species from existing ones
What is allopatric speciation
when a population becomme reproudctily isolated through geographical isolation and natural selection
What is sympatric speciation
when a population becommes reporoudctivly isolated wihtout a geograhical barieer, this can be because of random mutaions causing mechanical, seasonal or behavioural changes
What is sympatric speciation
when a population becommes reporoudctivly isolated wihtout a geograhical barieer, this can be because of random mutaions causing mechanical, seasonal or behavioural changes
How would reproductive isolation occur
- Seasonal: different flowering or mating seasons
- mechanical: they may have chnages in genatalia to prevent successful breeding
- Behavioural: courting rituals aren’t the same etc
What is artifical selection
process where humans choose organisms with desirable traits and selectively breed them together to ensure desirable traits are expressed over time and over many generations
