Selection, speciation and evolution

what is genetic diversity

the number of different alleles of genes in a population

what 4 things cause genetic variation in a population

• independent segregation

• crossing over of alleles

• random fusion of gametes

• random mutation

define population

a group of individuals of the same species that live in the same space and can interbreed

what 4 reasons may allow an individual to have better survival chances due to their genotype

• competition

• predation

• disease

• changes in the environment

what happens to the frequency of advantageous alleles in a population over time

they increase in frequency

what is directional selection

where a selection pressure favours one extreme over the other extreme and moderate characteristics

what is an example of directional selection

antibiotic resistance in bacteria

how does the phenotype characteristic mean and median shift with directional selection

shifts towards the favoured extreme

what does the graph for directional selection look like

what is stabilising selection

where selection pressures favour a non-extreme median phenotype

how does the data change with stabilising selection

the mode stays the same but the mode frequency increases

name an example of stabilising sekection

birthweight

what does a graph look like for stabilising selection

name 3 difference sbetween stabilising and direvtional selection

• the mode changes for direction selection but doesn’t for stabilising

• the mode stays the same frequency with direction but increases with stabilising

• with directional 1 extreme is at a disadvantage but with stabilising both extremes are at a disadvantage

what is disruptive selection

when individuals with extreme traits are favoured over individuals in the middle of the trait distribution

describe the shape of the disruptive selection graph

a bi-modal, two peaked curve, in which the two extremes create their own curve

draw a graph for disruptive distribution

what is speciation

when new species are derived from one existing species

what is allele frequency

how often a particular allele occurs within a population

define gene pool

all of the alleles of all the individuals in a population at a given time

what is allopatric speciation

when a new species forms while geographically isolated from its parent population

what is sympatric speciation

a subset of a population forms a new species with reproductive isolation not geographic isolation

explain how geographical isolation leads to allopatric isolation

• two species become reproductively isolated via geographical isolation

• there is genetic variation in both populations due to random mutation of DNA

• different environmental conditions create different selection pressures

• natural selection occurs, and individuals with the advantageous alleles are more likely to survive and breed

• different favourable alleles are passed on to offspring, and this leads to different changes in allele frequencies

• eventually members of the separate population will be unable to breed successfully tto produce fertile offspring

what is polyploidy

possessing more than 2 sets of chromosomes

what can cause reproductive isolation

• habitat preference

• polyploidy

• morphology

• behaviour

explain how sympatric speciation occurs

• there is no geographical isolation between the two populations

• there is genetic variation within the community due to random gene mutation

• this leads to reproductive isolation

• different alleles of each population increase in frequency

• disruptive natural selection occurs as there is a shift towards each extreme of the phenotype

• eventually each species cannot interbreed to produce fertile offspring