paper 2: Evolution May Lead to Speciation

Question 1

how does natural selection cause populations of species to become better adapted to thier environment

Answer 1

• random mutation results in a new allele
• gives organism an advantage with certain selection pressure
• organisms with allele more likely to survive and reproduce
• offspring inherit advantageous allele
• allele freuence increases over time
• causing direction/ stabilising/ disruptive selection

Question 2

what factors cause variation

Answer 2

genetics
environment

Question 3

whta produces further genetic variation

Answer 3

• meiosis and the random fertilisation of gametes during sexual reproduction

Question 4

decsribe discontinuous variation

Answer 4

• only discrete categories
• results from genetics only
• environment has little/ no influence

Question 5

draw a graph showing discontinuous variation

Answer 5

Question 6

describe continuous variation

Answer 6

• can take any value in any range
• results from many different genes
• environmental factors have a large impact

Question 7

draw a graph showing continuous variation

Answer 7

Question 8

what is a phenotype

Answer 8

the appearance of a characteristic due to the expression of genetic constitution and interaction with the environment

Question 9

what causes variation in phenotyoe

Answer 9

• mutations which create new alleles which produce non-functional proteins

Question 10

what is directional selection

Answer 10

• selection pressure that favours the extreme phenotype

Question 11

give an example of directional selection

Answer 11

antibiotic resistance in bacteria

Question 12

draw a graph showing directional selection

Answer 12

Question 13

what happens to allele frequenceis in directional selection refering to antibiotic resistant bacteria

Answer 13

• resistant allele increases overtime as it survives and reproduces so gets passed down

Question 14

what is stabilising selection

Answer 14

• selection spressure at both ends of distribution
• favours the intermediate phenotype and eliminates the extreme

Question 15

example of stabilising selection

Answer 15

human birth mass

Question 16

explain what happens to allele frequencies of stabilising selection using human birth mass

Answer 16

• small babies struggle to regulate body temperature due to a large SA:V ration
• large babies during birth so intermediate is favoured and normal birth mass allele frequency increases

Question 17

draw a graph showing stabilising selection

Answer 17

Question 18

what is disruptive selection

Answer 18

selection pressure favours both extremes of phenotype

Question 19

give an example of disruptive selection

Answer 19

• finches with large beaks feed on large seeds and finches with small beaks feed on small seeds

Question 20

what is speciation

Answer 20

the process through which new species arise

Question 21

what is a gene pool

Answer 21

all alleles of all the genes in a population

Question 22

what is allopatric speciation

Answer 22

2 populations of same species become geographically isolated from eachother so cannot interbreed

Question 23

model answer for allopatric speciation

Answer 23

• populations of same species become geographically isolated
• they cannot interbreed so forms separate gene pools
• areas have different selection pressures
• in each population mutations occur and form new alleles
• different alleles passed onto offspring
• allele frequency chnages over time
• when barries is removed the populations cannot interbreed to produce fertile offspring

Question 24

what is sympatric speciation

Answer 24

individuals become reproductively isolated from oher individuals in the same area

Question 25

model answer for sympatric speciation

Answer 25

- occurs within the same area - mutations form different alleles in population - populations become reproductively isolated - offspring inherit different alleles changing the allele frequency over many generations - causes disruptive selection - populations cannot interbreed to produce fertile offspring

Question 26

what is genetic drift

Answer 26

in small populations, by chnace one allele is inherited more often and becomes more frequent

Question 27

what is the difference between genetic drift and natural selection

Answer 27

- natural selection only causes alleles and phenotypes to become more common if they increase chance of survival - genetic drift makes alleles become more common by chance