20. Natural selection and speciation

Question 1

What is natural selection

Answer 1

the process that leads to evolution

Question 2

What is evelution

Answer 2

the change in the frequency of alleles within a population over many generations.

Question 3

What causes changes to allel frequencioes

Answer 3

differential reproductive success – some phenotypes are more likely to survive and reproduce than others

Question 4

What are the causes of variation in any population

Answer 4

· mutations

· meiosis

· Random fusion of gametes

Question 5

What results in selection pressures

Answer 5

Predation, disease, competition and changes in the environment
giving some phenotypes a selective advantage acting as a trigger for natural selection to occur.

Question 6

What is the process of natural selection

Answer 6

· There is variation in a population.
· is due to random mutations giving rise to new alleles of a gene.
· Organisms that have advantageous alleles, will have a phenotype that give them a selective advantage
· Organisms with advantageous alleles are more likely to survive to reproduce
· These organisms are more likely to pass on advantageous alleles to the next generation
· causes an increase in the frequency of the advantageous allele in that population over many generations.

Question 7

What is an example of anotomical adaptations

Answer 7

Changes to the organisms body, such as beak shape

Question 8

What is an example of physiological adaptations

Answer 8

Haemoglobin with a different oxygen affinity

Question 9

What is an example of behavioural adaptations

Answer 9

Better food search strategies / more elaborate songs in whales

Question 10

What are the different types of selection

Answer 10

1. Directional.
2. Stabilising .
3. Disruptive.

Question 11

What is directional selection

Answer 11

Occurs when the environment changes
acts against one of the extreme phenotypes and selects the other. This results in an increase in the frequency of alleles resulting in the most successful phenotype.

Question 12

What is stabilising selection

Answer 12

occurs in an unchanging environment
type of selection acts against both the extremes in a range of phenotype. Acts to prevent change

Question 13

What is disruptive selection

Answer 13

occurs in a fluctuating environment
individuals with both extremes of a phenotype have a selective advantage over those in the middle, so both are selected. The intermediate phenotypes are selected against.

Question 14

What is a species

Answer 14

A group of organisms with similar characteristics that can interbreed to produce fertile offspring

Question 15

What is speciation

Answer 15

Speciation is a process whereby one gene pool gives rise to more than one gene pool.

Question 16

What are the types of speciation

Answer 16

Allopatric speciation
Sympatric speciation

Question 17

What is allopatric speciation

Answer 17

occurs when two populations of the same species become geographically separated by a physical barrier
prevent the separated populations from interbreeding.

Question 18

What happens to genetic differences in allopartic speciation

Answer 18

genetic differences between the populations increase through selection due to the different environmental conditions so different selection pressures. Eventually, the two populations are unable to interbreed and have become distinct species

Question 19

What is sympatric speciation

Answer 19

the two populations may inhabit the same area, but still evolve into 2 different species
occur due to random mutations leading to differences that prevent individuals with the mutation from breeding with other members of the population that do not carry the mutation. This is called reproductive isolation

Question 20

What are causes of sympatric speciation

Answer 20

Seasonal / temporal isolation
Mechanical isolation
Behavioural isolation

Question 21

How does sesonal isolation cause sympatric speciation

Answer 21

members of the two populations reproduce at different times of the year

Question 22

How does mechanical isolation cause sympatric speciation

Answer 22

anatomical differences may prevent mating occurring

Question 23

How does behavioural isolation cause sympatric speciation

Answer 23

For example - members of the two populations have different courtship patterns

Question 24

How does evolution occur via genetic drift

Answer 24

chance rather than environmental factors dictate which alleles are passed on. Genetic drift can lead to differences in allele frequencies between two isolated populations. Over time, this could lead to reproductive isolation and speciation
The smaller a population the bigger the impact these chance changes in allele frequency will have – hence evolution often occurs more rapidly in smaller populations.