1.6 - Evolution

Question 1

What is evolution

Answer 1

Evolution is the change in organisms over generations as a result of genomic variation

Question 2

What types of gene transfer are there

Answer 2

Vertical and horizontal

Question 3

What is the difference between vertical inheritance and horizontal gene transfer

Answer 3

Vertical is the transfer of genetic material from one generation to the next

Horizontal is the transfer of genetic material within the same generation

Question 4

What are the pros and cons of horizontal gene transfer

Answer 4

HGT is more rapid and can make evolution much quicker

Genetic material passed on through HGT haven’t been ‘tried and tested’ and therefore can be risky

Question 5

What is selection

Answer 5

Selection is the non-random process by which DNA sequences in a population will either:

• increase because they’re selected for
• decrease because they’re selected against

Question 6

What types of selection are there

Answer 6

Natural selection and sexual selection

Question 7

What happens during natural selection

Answer 7

Only organisms with the best combination of genes for their environment will survive.

This means that better gene combinations are passed on to the next generation.

Organisms with less useful genes will die out and not pass on their alleles.

If natural selection operates over millions of years it can give rise to a new species.

Question 8

Explain how sexual selection works

Answer 8

Males have a lot of sperm and females have limited eggs therefore females chose who they want to mate with.

Males compete through fighting/rituals and the ones that perform best win.

Females select a male based on the high quality of traits on display.

Then they can pass on their alleles to the next generations.

Question 9

What are the 3 ways that natural selection can affect the frequency of polygenic traits?

Answer 9

Stabilising selection

Directional selection

Disruptive selection

Question 10

Describe stabilising selection

Answer 10

Cells extremes from the population and leads to a decrease in diversity

Occurs in unchanging environments to maintain the best adapted genes

Question 11

Describe directional selection

Answer 11

Favours characteristics that were initially less common

Common during a period of environmental change

Question 12

Describe disruptive selection

Answer 12

Extreme versions of a characteristic are favoured rather than the intermediates

Results in population becoming split into distinct groups

Question 13

What is a gene pool

Answer 13

A gene pool is the total of all the different alleles present in a population

Question 14

What is genetic drift

Answer 14

Genetic drift is the random increase/decrease of alleles due to a non-representative sample of the whole population being passed on to the offspring

Question 15

What is the founder effect

Answer 15

This is a special case of genetic drift where a small group of individuals colonise a new habitat

Question 16

What is speciation

Answer 16

Speciation is the formation of a new biological species

Question 17

When does speciation occur

Answer 17

Speciation occurs when circumstances arise that interrupt gene flow between two populations causing their gene pool to diverge to the point where they cannot successfully interbreed

Question 18

What are the 2 types of speciation

Answer 18

Allopatric speciation

Sympatric speciation

Question 19

Describe allopatric speciation

Answer 19

Gene flow between populations is interrupted by a geographical barrier that physically isolated populations

Question 20

Describe sympatric speciation

Answer 20

Gene flow is interrupted by a behavioural or ecological barrier that genetically isolates populations