Variation and evolution

Question 1

What factors produce variation between individuals?

Answer 1

Both genetic and environmental factors produce variation.

Question 2

Name the types of variation.

Answer 2

• Continuous and discontinuous.

- Heritable and non-heritable.

Question 3

What is discontinuous variation?

Answer 3

• Type of variation that can be categorised, e.g. blood group.
• A characteristic can only appear in discrete values.
• It is influenced by one or two genes and environmental factors have little effect.

Question 4

What is continuous variation

Answer 4

• Type of variation that cannot categorised, e.g. height.
• Produces a continuous range in which a characteristic can take any value.
• It is influenced by multiple genes and is often significantly affected by environmental factors.

Question 5

Compare heritable and non-heritable variation.

Answer 5

Heritable variation is the genetic differences between individuals whereas non-heritable variation is acquired differences in the phenotypes of individuals that cannot be inherited.

Question 6

What is evolution?

Answer 6

• The change in allele frequencies in a gene pool of a population over time.
• Occurs due to natural selection.

Question 7

How does natural selection cause a change in allele frequencies over generations?

Answer 7

Organisms with advantageous characteristics are more likely to survive and pass their favourable alleles to offspring. Frequency of unfavourable alleles decreases.

Question 8

What are selection pressures?

Answer 8

• Environmental factors that drive evolution by natural selection and limit population sizes.
• They can change the frequency of alleles in a population.

Question 9

Give examples of selection pressures.

Answer 9

• Predation.
• Disease.
• Competition (for food, habitats, mates).
• Environmental conditions, e.g. temperature.

Question 10

How can allele frequencies be expressed?

Answer 10

Expressed as a percentage or proportion of the total number of alleles for that gene.

Question 11

State the two types of competition.

Answer 11

• Interspecific (between members of different species).

- Intraspecific (between members of the same species).

Question 12

Define gene pool.

Answer 12

All of the different versions of genes (alleles) in the individuals that make up a population.

Question 13

What is genetic drift?

Answer 13

Variations in allele frequencies in small populations due to chance (rather than as a result of selection pressures).

Question 14

What is meant by the founder effect?

Answer 14

When a small number of individuals become isolated, forming a new population with a limited gene pool. Allele frequencies are not reflected of the original populations.

Question 15

What is the Hardy-Weinberg principle?

Answer 15

A model that allows the estimation of the frequency of alleles in a population, as well as whether allele frequency is changing over time.

Question 16

State the assumptions made by the Hardy-Weinberg principle.

Answer 16

• No mutations occur to create new alleles.
• No migration in or out of the population.
• No selection, alleles are all equally passed on to the next generation.
• Random mating.
• Large population.

Question 17

Explain the Hardy- Weinberg equation for calculating allele frequency.

Answer 17

The frequencies of each allele for a characteristic must be add up to 1.0 giving the equation: p + q = 1.0
Where p = frequency of the dominant allele. and q = frequency of the recessive allele.

Question 18

Explain the Hardy- Weinberg equation for calculating genotype frequency.

Answer 18

The frequencies of each genotype for a characteristic must add up to 1.0 giving the equation: p(squared) + 2pq = q(squared) = 1.0
Where p (squared) = frequency of homozygous dominant, 2pq = frequency of heterozygous, and q (square) = frequency of homozygous recessive.

Question 19

Define speciation.

Answer 19

The formation of new species due to the evolution of two reproductively separated populations.

Question 20

Causes of speciation

Answer 20

• Genetic drift in isolated population.
• Founder effect.
• Natural selection.

Question 21

What are the two types of speciation?

Answer 21

• Allopatric speciation (when two populations become geographically isolated).
• Sympatric speciation (when to populations within the same area become reproductively isolated).

Question 22

Outline geographical isolation.

Answer 22

A physical barrier (such as a river or mountain) separates two populations of the same species.

Question 23

Name the potential isolation mechanisms in sympatric speciation.

Answer 23

• Morphological isolation.
• Seasonal isolation.
• Behavioural isolation.
• Gametic isolation.
• Hybrid sterility.
• Hybrid inviability.

Question 24

What is morphological isolation?

Answer 24

The reproductive isolation of two populations due to the incompatibility of their reproductive systems.

Question 25

What is behavioural isolation?

Answer 25

The reproductive isolation of two populations due to differences in their behaviour (such as different mating rituals).

Question 26

Describe seasonal isolation?

Answer 26

The reproductive isolation of two populations due to differences in their breeding seasons.

Question 27

Describe hybrid inviability.

Answer 27

• Post-zygotic barrier.

- Successful fertilisation but embryo cannot develop into a living organism.

Question 28

What is hybrid sterility?

Answer 28

The formation of sterile hybrid offspring from the reproduction of individuals of different species.

Question 29

Why may the reproduction of individuals of different species produce sterile offspring?

Answer 29

The chromosomes sets from each parent differ so are unable to pair up during meiosis.

Question 30

Give an example of a sterile hybrid and fertile hybrid.

Answer 30

• Sterile hybrid = mule.

- Fertile hybrid = wheat.

Question 31

What is gametic isolation?

Answer 31

• Prezygotic barrier.

- Successful fertilisation does not occur.