populations and evolution

Question 1

what are the different types of variations

Answer 1

there is phenotypic variation within every population due to a combination of genetic and environmental factors

Question 2

what is the primary source of genetic variation

Answer 2

the primary source of genetic variations is due to mutation producing different alleles

Another source of genetic variation is random fertilisation of gametes independent segregation and crossing over which leads to recombinant alleles

Question 3

what are the causes of environmental varitaion

Answer 3

disease predation and competition

Question 4

How does selection affect allele frequencies

Answer 4

selection has an effect on allele frequencies

This is because not all individuals can survive and reproduce due to factors such as disease, predation and completion

organisms with phenotypes providing a selective advantage are more likely to produce more offspring and pass on their favourable alleles to the next generation

Therefore, allele frequencies change over time. This process is called evolution

Question 5

what are the different types of selection

Answer 5

directional selection

stabilising selection

disruptive selection

Question 6

what is directional selection

Answer 6

selection favours one extreme phenotype

This can affect a distribution curve as it normally shifts to the right

The new allele arises due to a mutation
Organisms that have this allele are at an advantage, this causes the normal distribution to shift in the direction of the favoured trait which is normally to the right

Question 7

what is stabilising selection

Answer 7

selection favours the average phenotype allele e.g. birth weight in babies

Babies that have an average birth weight are more likely to survive as they are less likely to be susceptible to complications
The curve becomes more narrow as the highest frequency is the average trait

Question 8

what is disruptive selection

Answer 8

it is a selection that favours both extreme phenotype/ alleles but at different times due to environment factors

Question 9

what is speciation

Answer 9

speciation is the evolution of new species form existing ones

New species arise when genetic different due to selection lead to an inability of members of the population to interbreed and produce fertile offspring as genetic differences become usually different

Question 10

what is allopratic speciation

Answer 10

1. population becomes geographically seperated e.g. from the formation of a river or mountain range
2. separated populations are unable to reproduce due to the physical barrier
3. the seperate population, have different environment/ selection pressures, so will accumulate different beneficial mutation over time ti help them survive. This leads to different reproductive success, so changes in allele frequencies
4. the two populations eventually become so genetically they can’t reproduce to produce fertile offspring (reproductive isolation) so are now classed as different species

Question 11

what is sympathetic speciation

Answer 11

population become reproductively isolated due to differences in behaviour
e.g. a random mutation could influence a reproductive behaviour e.g. individuals fertile at different times of the year or different courtship behaviours so individuals will not reproduce together

overtime, their DNA becomes so different so individuals are no longer able to reproduce to produce fertile offspring, so are classed as 2 different species

Question 12

what is genetic drift

Answer 12

genetic drift change in allele frequency within a population between generations this will be by chance and not selection pressures

Question 13

what can of genetic drift leads to evolution

Answer 13

continual genetic drift leads to evolution

Question 14

how does genetic drift affect small populations

Answer 14

genetic drift has a larger effect in small populations as allele frequency changes have a larger impact, so evolution occurs more rapidly in small populations