Selection and Speciation

Question 1

Can you describe phenotypic variation due to genetic factors?

Answer 1

Mutation – generates new alleles
Mixing of alleles - meiosis
Random fertilisation

Question 2

Can you describe phenotypic variation due to environmental influences?

Answer 2

Length of sunlight hours (seasonal)
Supply of nutrients
Availability of water
Temperature range
Oxygen levels

These factors will affect the potential phenotype that is determined by genetics

Question 3

Define a gene pool

Answer 3

All the alleles of all the genes of all the individuals in a population at a given time

Question 4

Can you explain the role of variation in natural selection:

Question 5

Can you explain the role of overproduction of offspring in natural selection:

Question 6

What is selection?

Answer 6

Phenotypic selective advantages are more likely to survive reproduce and pass on favourable alleles to offspring, increasing allele frequency of many generations.

3 types of selection: Disruptive, directional, stabilising.

Question 7

What environmental factors exert selection pressure?

Answer 7

predation
disease
availability of resources
climate
competition

Question 8

Why is genetic drift only important in small populations?

Answer 8

the change has a greater influence than in large populations (doesn’t spread out evenly across the population)

Question 8

Can you describe stabilising selection?

Answer 8

typically happens in an unchanging environment
favours individuals with phenotypes close to the mean and selects against extreme phenotypes
the mean remains the same

Question 9

Can you describe disruptive selection?

Answer 9

favours individuals with extreme phenotypes and selects against those with phenotypes close to the mean

Question 10

Can you describe directional selection?

Answer 10

typically happens in changing environments
favours one extreme phenotype and selects against all other phenotypes
the mean shifts

Question 11

How does selection affect allelic frequencies?

Answer 11

Selection pressures lead to adv alleles being passed on to offspring, increasing allele frequency

Question 12

How are new species formed?

Answer 12

Changes in allele frequencies in isolated populations result in new species forming over long periods of time that cannot interbreed with the previous population to produce fertile offspring.

Question 12

What is a species?

Answer 12

A group of individuals that can interbreed to produce fertile offspring.

Question 13

Describe allopatric speciation:

Answer 13

New species form from different populations/groups/gene pools
In different areas/ from isolated population

Geographical isolation
Separate gene pools with no gene flow Variation due to random mutation Different selection pressures
Differential reproductive success
Passing on favourable alleles Increasing allele frequency
Diverged gene pools means populations cannot interbreed to produce fertile offspring

Question 14

Describe sympatric speciation:

Answer 14

Formation of new species / reproductive isolation
From a population living in the same area/ no geographical isolation.

Occuring in the same habitat
Mutations cause different flowering times. Reproductive isolation
Gene pools remain separate,
no gene flow.
Different alleles passed on
Changes in allele frequency
Disruptive natural selection.
Different populations cannot interbreed to produce fertile offspring.

Question 15

Define genetic drift

Answer 15

In genetic drift, the alleles are passed on by random chance. It is easier to see the effect of genetic drift within a small population.

Question 16

Isolating mechanisms

Answer 16

Temporal
Organisms breed at different times of year.

Ecological
Different habitats within same area.

Behavioural
Different behaviour patterns e.g. courtship behaviour.

Mechanical
Anatomical differences making it impossible for gametes to come together.

Gametic
Incompatibility (genetic or physiological) between gametes prevent hybrid from forming.

Hybrid sterility
Organisms interbreed but offspring are infertile:
E.g. horse and donkey can produce mule but mule is infertile.

Question 17

Define genetic drift.

Answer 17

Genetic drift is change in allele frequencies in a population from generation to generation that occurs due to chance events. (samping error).

May lead to loss of some alleles and fixation of other alleles

Can have major effects when:

Natural disaster reduces population (bottleneck effect)

Small group splits off from main population to found a colony (founder effect).