7.3 Evolution may lead to speciation

Question 1

what are phenotypes

Answer 1

a results of the alleles (genotype) of an individual and environmental factors

Question 2

what are causes of genetic variation

Answer 2

• mutation
• crossing over in meiosis
• independent segregation in meiosis
• random fertilisation of gametes

Question 3

what is evolution

Answer 3

the change in phenotypes of a population

Question 4

what does evolution occur from

Answer 4

a change in allele frequencies in a population

Question 5

why do allele frequencies change

Answer 5

due to differential survival and reproduction e.g. natural selection

Question 6

why does environmental pressure change

Answer 6

a change in predation or disease, or a change in resources available which affects competition

Question 7

why do small populations experience more rapid changes in allele frequency

Answer 7

genetic drift
- fertilisation will change alleles as it is random
- the changes are bigger when there are fewer fertilisation events occuring

Question 8

how do species characteristics change

Answer 8

• all organisms have a range of phenotypes
• for polygenic traits, the observed phenotypes show normal distribution
• different types of selection occur to accommodate to the environment

Question 9

what are the different types of selection

Answer 9

• stabilising
• directional
• disruptive

Question 10

what is stabilising selection

Answer 10

• the intermediate phenotypes are best adapted to survival
• they become more common and the extreme phenotypes disappear

Question 11

what is directional selection

Answer 11

• an extreme phenotype is best adapted for survival in the environment, so is advantageous
• the extreme phenotypes become more common
  e.g. antibiotic resistance

Question 12

what is disruptive selection

Answer 12

• the population experiences two different environmental pressures
• 2 extreme alleles are advantageous in these 2 environments
• the extreme phenotypes become more common, one in each environment and the intermediate phenotypes become more common
• this results in SPECIATION

Question 13

what is speciation

Answer 13

the development of 2 species from a single original species

Question 14

how does speciation occur

Answer 14

• the 2 populations become reproductively isolated
• each population experiences a different selection pressure
• variation in each population due to mutation
• different alleles are advantageous -> so those with the advantageous alleles survive and reproduce
• allele frequency changes in each population
• eventually the populations cannot interbreed to produce successful offpsring

Question 15

what is reproductive isolation

Answer 15

there is no gene flow between 2 populations

Question 16

what are the types of speciation

Answer 16

• allopatric
• sympatric

Question 17

what is allopatric speciation

Answer 17

geographical isolation (the 2 populations are physically separated)

Question 18

what is sympatric isolation

Answer 18

behavioural changes occur e.g. frequency of bird calls so the 2 populations cannot breed