Variation and Evolution

Question 1

What factors produce variation between individuals?

Answer 1

What factors produce variation between individuals? 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.

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 all alleles for that
gene.

Question 11

State the two types of competition.

Answer 11

Interspecific
Intraspecific

Question 12

What is interspecific competition?

Answer 12

A type of competition that takes place between members of different species.

Question 13

What is intraspecific competition?

Answer 13

A type of competition that takes place between members of the same species.

Question 14

Define gene pool

Answer 14

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

Question 15

What is genetic drift?

Answer 15

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

Question 16

What is meant by the founder effect?

Answer 16

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

Question 17

What is the Hardy-Weinberg principle?

Answer 17

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 18

State the assumptions made by the Hardy-Weinberg principle.

Answer 18

• 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 19

Explain the Hardy-Weinberg equation for calculating allele frequency.

Answer 19

The frequencies of each allele for a characteristic must 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 20

Explain the Hardy-Weinberg equation for calculating genotype frequency.

Answer 20

The frequencies of each genotype for a characteristic must add up to 1.0 giving the equation: p2 + 2pq + q2 = 1.0
where p2 = frequency of homozygous dominant, 2pq = frequency of heterozygous, and q2 = frequency of homozygous recessive

Question 21

Define speciation.

Answer 21

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

Question 22

Why may speciation occur?

Answer 22

Genetic drift in isolated population
Founder effect
Natural selection

Question 23

What are the two types of speciation?

Answer 23

• Allopatric speciation
• Sympatric speciation

Question 24

What is the term for speciation that occurs when two populations become geographically isolated?

Answer 24

Allopatric speciation

Question 25

What is the term for speciation that occurs when two populations within the same area become reproductively isolated?

Answer 25

Sympatric speciation

Question 26

Outline geographical isolation.

Answer 26

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

Question 27

Name the potential isolation mechanisms in sympatric speciation.

Answer 27

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

Question 28

What is morphological isolation?

Answer 28

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

Question 29

What is behavioural isolation?

Answer 29

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

Question 30

Describe seasonal isolation.

Answer 30

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

Question 31

Describe hybrid inviability.

Answer 31

• Post-zygotic barrier
• Successful fertilisation but embryo cannot develop into a living organism

Question 32

What is hybrid sterility?

Answer 32

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

Question 33

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

Answer 33

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

Question 34

Give an example of a sterile hybrid and a fertile hybrid.

Answer 34

• Sterile hybrid - mule
• Fertile hybrid - wheat

Question 35

What is gametic isolation?

Answer 35

Pre-zygotic barrier
* Successful fertilisation does not occur