Evolution

Question 1

How does variation in a species happen

Answer 1

Mutations
Alleles
Crossing over and independent segregation
Environmental- climate, food, lifestyle

Question 2

Define evolution

Answer 2

The frequency of an allele in a population changes over time

Question 3

Explain evolution by natural selection

Answer 3

Individuals vary due to different alleles
Selection pressures create a struggle for survival
Individual with beneficial alleles not the selection pressure are more likely to survive and reproduce
Passing on the successful genes
A greater proportion of the next gen will have the beneficial alleles
And are more likely to survive and reproduce
Increasing the allele frequency in the gene pools

Question 4

What is stabilising selection

Answer 4

Alleles for a phenotype in the middle ground are favoured so are more likely to survive and reproduce

Question 5

Where does stabilising selection occur

Answer 5

The environment isn’t changing and reduces the range of phenotypes

Question 6

What is directional selection

Answer 6

Individuals with alleles for an extreme phenotype are more likely to survive and reproduce

Question 7

Why does directional selection happen

Answer 7

Environmental change

Question 8

What is disruptive selection

Answer 8

Individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce

Question 9

When does disruptive selection happen

Answer 9

The environment favours more than one phenotype

Question 10

What is assortative breeding

Answer 10

Non random

Leads to 2 different breeding populations

Question 11

What is speciation

Answer 11

The development of a new species from an existing species

Question 12

Describe speciation

Answer 12

Populations of the same species become reproductively isolated
Causing changes in allele frequency
Changing the phenotype
The 2 populations can no longer interbreed to produce fertile offspring

Question 13

What is allopatric speciation

Answer 13

Populations separated by a physical barrier

So the populations are geographically isolated
And experience slightly different environmental conditions
So experience different selection pressures
And different phenotypes are beneficial
So change allele frequency and phenotype frequency
Until the 2 populations are so different they are reproductively isolated

Question 14

Why does allele frequency change

Answer 14

Different alleles are advantageous for different populations in different environments.
Mutations
Genetic drift

Question 15

What is sympatric speciation

Answer 15

Populations don’t have to be geographically isolated

Members of the population have random mutations preventing them breeding and becoming reproductively isolated

Question 16

How is polyploidy an example or sympatric speciation

Answer 16

Most eurkaryptic orgs have a diploid number of chromosomes
Mutations create polyploid organisms
That can’t reproduce sexually to give fertile offspring
So are reproductively isolated
If the polyploid org reproduces asexually to give fertile offspring a new species will be created

Question 17

When can speciation only occur

Answer 17

If the change isn’t fatal

Question 18

When does reproductive isolation occur

Answer 18

When changes in alleles ans phenotypes prevent orgs reproducing successfully

Question 19

What is an example of Seasonal reproductive isolation

Answer 19

Individuals of the same species develop different mating/flowering seasons

Question 20

What is an example of mechanical reproductive isolation

Answer 20

Changes to genitalia

Question 21

Give an example of behavioural reproductive isolation

Answer 21

Individuals of the same species develop different courtship rituals that aren’t attractive to the main populations

Question 22

Explain genetic drift

Answer 22

Individuals in a population show genotype variation
By chance the allele for 1 genotype is passed on more than the other
So the allele frequency of that genotype increases
Changes in allele frequency in 2 isolated populations could lead to reproductive isolation and speciation

Question 23

When does genetic drift have a bigger impact

Answer 23

In smaller populations because chance has a greater influence
As large populations chance variations even out