3.7.3 Evolution and speciation

Question 1

What is the primary source of genetic variation?

Answer 1

mutation

Question 2

What are the 3 main causes of genetic variation?

Answer 2

1. Mutations
2. Meiosis
3. Random fertilisation of gametes

Question 3

How does the environment cause variation?

Answer 3

affects the way the organism’s genes are expressed

Question 4

What are some environmental influences on variation examples?

Answer 4

temperature
rainfall
sunlight
soil conditions
pH
food availability

Question 5

What is a selection pressure?

Answer 5

the environmental factors that limit the population of a species

Question 6

Give 3 examples of selection pressure

Answer 6

predation
disease
competition

Question 7

Selection pressures determine…

Answer 7

the frequency of all alleles within the gene pool

Question 8

What is a gene pool?

Answer 8

total number of all the alleles of all the genes of all the individuals within a particular population at a given time

Question 9

What are the 4 key marking points for natural selection?

Answer 9

1. Variation - caused by a mutation, creating an alternative allele
2. Selection pressure - makes mutated allele advantageous
3. Individuals with mutated allele survive to reproduce and pass on allele to offspring
4. Increased allele frequency in population

Question 10

What is stabilising selection?

Answer 10

preserves the average phenotype, selection against extreme phenotypes

Question 11

What is directional selection?

Answer 11

selection for one extreme phenotype

Question 12

What is disruptive selection?

Answer 12

favours individuals with extreme phenotypes (rather than those with phenotypes around the mean)

Question 13

When does disruptive selection occur?

Answer 13

when an environmental factor takes 2 or more distinct forms

Question 14

What is allele frequency?

Answer 14

the number of times an allele occurs within the gene pool

Question 15

Evolution by natural selection is…

Answer 15

the change in the allelic frequencies within a population

Question 16

What is speciation?

Answer 16

the evolution of new species from existing ones

Question 17

What is the definition of a species?

Answer 17

a group of similar organisms (share the same genes but different alleles) that can breed together to produce fertile living offspring

Question 18

Members of the same species are ……… separated from other species?

Answer 18

reproductively

Question 19

Genetic drift can take place in…

Answer 19

small populations
(as there are a smaller variety of alleles - smaller genetic diversity)

Question 20

What does allopatric speciation refer to?

Answer 20

speciation as a result of 2 populations becoming geographically separated

Question 21

What is meant by geographical separation?

Answer 21

physical barrier between 2 populations - prevents them interbreeding
(e.g. oceans, rivers, mountain ranges)

Question 22

Why does geographical isolation cause speciation?

Answer 22

-different environmental conditions on either side of barrier
-2 populations will evolve differently
-different adaptions
-leads to reproductive isolation

Question 23

What is meant by sympatric speciation?

Answer 23

speciation that results within a population in same area, leading to reproductive separation

Question 24

Speciation 6 mark answer (allopatric)

Answer 24

1. Geographical isolation
2. Gene pools are separated, hence there is no gene flow
3. Populations experience different selection pressures (due to diff environmental conditions)
4. Variation due to mutations in different populations
5. Change in allele frequency
6. Eventually different species, as they cannot interbreed to produce fertile offspring