7.3 Evolution

Question 1

Two types of variation

Answer 1

• Genetic variation
• Environmental variation

Question 2

3 causes of genetic variation

Answer 2

• Mutation
• Meiosis
• Random fertilisation

Question 3

Explain how mutations cause genetic variation

Answer 3

Mutations are changes in the base sequence. Changes may cause the structure of proteins encoded by DNA to be altered.

Question 4

Explain how meiosis causes genetic variation

Answer 4

Independent segregation:
- The chromosomes in a pair of homologous chromosomes are randomly separated and this creates genetic variation.
Crossing over:
- The genes on homologous chromosomes are reshuffled through a process called crossing over.
- Crossing over produces a new combinations of genes. This increases genetic variation.

Question 5

Explain how random fertilisation causes genetic variation

Answer 5

During sexual reproduction, the gametes of two unrelated individuals are fused to produce a diploid individual.
Random fertilisation produces genetic variation because pairs of chromosomes from two separate individuals are combined.

Question 6

3 factors that affect capability to survive

Answer 6

• Predation
• Disease
• Competition

Question 7

Competition between different species is called…

Answer 7

Interspecific competition

Question 8

Competition between individuals in the same species is called…

Answer 8

Intraspecific competition

Question 9

What is a selective advantage

Answer 9

Genetic variation exists between individuals in a population.
Some individuals will be more likely to survive (e.g. by being better at fighting disease) than others.
Individuals that are better at surviving than others have a selective advantage.

Question 10

What are individuals with a selective advantage more likely to do?

Answer 10

Individuals with a selective advantage are more likely to survive to reproduce than others.
This means that the genes of an individual with a selective advantage are more likely to be passed onto offspring than the genes of an individual without a selective advantage.

Question 11

What causes allele frequencies to increase

Answer 11

Individuals with a selective advantage are more likely to pass on their beneficial alleles than other individuals.
The next generation is more likely to have alleles that provide a selective advantage than alleles that do not.
This generation is also more likely to survive to reproduce and pass on their genes.
This causes the alleles that provide a selective advantage to increase in frequency in the population.

Question 12

What is natural selection

Answer 12

The process where the frequency of beneficial alleles increases over time is called natural selection.
Natural selection controls the frequency of alleles in a population.
If a harmful allele develops in an individual, this individual is less likely to survive and the harmful allele will decrease in frequency. This is also natural selection.

Question 13

What does the process of natural selection give rise to?

Answer 13

Evolution

Question 14

What is evolution?

Answer 14

The change in allele frequencies overtime. It is driven by natural selection.

Question 15

What is a selection pressure?

Answer 15

The selection pressure is an external factor that influences the reproductive success of an individual.

Question 16

What is stabilising selection?

Answer 16

Natural selection favours the average phenotype.
The selection pressures select against the extreme phenotypes.
Takes place in environments that do not change.

Question 17

What is directional selection?

Answer 17

Natural selection favours an extreme phenotype.
The selection pressures select against all other phenotypes.
Takes place after an environment has experienced a change.

Question 18

What is disruptive selection?

Answer 18

Natural selection favours the two extremes of a phenotype.
The selection pressures select against the average phenotype.
Takes place in an environment that favours more than one phenotype.

Question 19

What is speciation?

Answer 19

Speciation is where two new species arise from a single species. This happens when two populations are prevented from interbreeding.

Question 20

What is reproductive isolation?

Answer 20

Gene flow is the movement of alleles between a population. When two populations are reproductively isolated, the gene flow of the populations is restricted.
The two populations are said to be reproductively isolated.

Question 21

Explain the process of allopatric speciation

Answer 21

Population splits into two populations due to geographical isolation caused by environmental changes e.g. emergence of a river.
The different environments will have different conditions which provide different selection pressures.
Different selection pressures drive natural selection in different directions.
Natural selection causes changes in allele frequencies.
Eventually, allele frequencies will change so much so that the populations can no longer interbreed to produce fertile offspring and are no longer defined as the same species.

Question 22

Explain the process of sympatric speciation

Answer 22

In sympatric speciation, a population of species is reproductively isolated without geographical separation.
Reproductive isolation may arise where a mutation emerges in a population that prevents some members of the population from interbreeding with others.
Due to no interbreeding, allele frequencies change and over time the gene pools of the populations have changed so much so that they can no longer interbreed to produce fertile offspring and are no longer defined as the same species.

Question 23

Explain how genetic drift can bring about speciation

Answer 23

By chance, some alleles are passed onto offspring and some are not.
This causes random changes in the allele frequencies in the population.
This is called genetic drift.

When two populations are reproductively isolated, they are exposed to different selection pressures. These selection pressures drive the evolution of the two populations in different directions. This is called disruptive selection.
Genetic drift also contributes to the speciation by causing random changes in the allele frequencies of the two populations.
Because the two populations can no longer interbreed, the gene pools will become increasingly different. This causes speciation.

Question 24

Which populations does genetic drift affect the most?

Answer 24

Smaller populations as larger populations tend to dilute the effect of genetic drift in their large number of each allele.