8. Mechanisms of evolution Part 2

Question 1

Describe population bottleneck and give an example:

Answer 1

-Population bottleneck is observed when the population is reduced to small numbers due to a catastrophic event or period of adverse conditions and loses most of its genetic variation.
-The genetic variability in the population become low, meaning that even if the species recovers and goes on to grow in number, the new species’ members have less genetic variation than their ancestors.
-Makes such species more vulnerable to selecting agents in their environment and therefore more vulnerable to extinction
Eg. Cheetahs survived a severe bottleneck that increased the frequency of some deleterious alleles.

Question 2

What is the founder effect?

Answer 2

The effect on a population’s genetic makeup of the genetic material provided by the founders of the population.
-When small populations colonise in a new area, the individuals in that small colony are unlikely to have the same allele frequencies (genetic diversity) that you would find in the parent population’s gene pool.

Question 3

What are selection pressures?

Answer 3

Biotic (living) and abiotic (non-living) factors of the environment that can influence the survival and reproduction of a population.
-Favours the development of a particular trait

Question 4

List and describe 3 selection pressures:

Answer 4

• Competition: Food, water, shelter, mates
• Migration: Leads to deaths during journey
• Geographical features: Natural events can kill or split a population

Question 5

What does adaption refer to?

Answer 5

The ‘end’ result of a selection pressure for a particular trait over time.

• Feature which aids survival
• Gives a better chance of surviving to adulthood this a reproductive advantage – increased chance of passing on genes

Question 6

What does fitness refer to?

Answer 6

Physical and behavioural traits that enable organisms to survive and reproduce in their environment. Fitness arises through adaption.

Question 7

What is evolution and what does it require?

Answer 7

Changes that occur in the gene pool of a population over time – leads to the production of new species.
-Requires a change in the environment

Question 8

Describe the theory of natural selection:

Answer 8

• A population of organisms of a particular species will show variation
• Environmental change occurs
• Individuals with features that help them survive the new environment are selected for (fitter)
• Fitter individuals have increased survival rates and therefore increased rates of reproduction – they pass on characteristics to next generation

Question 9

Give an example of natural selection:

Answer 9

Bacterial resistance

1. Variation already existed in the population of bacteria
2. A selective pressure (antibiotics) were applied
3. Those bacteria that were resistant to the bacteria due to variation were more likely to survive (more fit), those less resistant were more likely to die
4. Resistant survivors go on to reproduce and pass their resistant alleles on to their offspring, increasing the frequency of resistance in the population

Question 10

What is allopatric speciation?

Answer 10

• When a large ancestral population is divided into smaller populations by physical separation through geographic isolation
• Gene flow is disrupted

Question 11

List some examples of allopatric speciation barriers:

Answer 11

• Water, for terrestrial organisms
• Land for aquatic organisms
• Mountains
• Continental drift
• Rising sea levels
• Climate change

Question 12

Describe the process of allopatric speciation:

Answer 12

1. Begins with an interbreeding population of one species
2. Population becomes divided by a geographic barrier
3. If the two environments (abiotic or biotic) are different there will be different selection pressures and the two populations will evolve differently.
4. Even if the barrier is removed, the two populations may be so different they can no longer interbreed – they are reproductively isolated; they are now different species

Question 13

What is artificial selection?

Answer 13

The process by which humans select and develop desireable traits in a species.

Question 14

What been the effect of the human (artificial) selection of animals? Give an example:

Answer 14

-Human selection of which animals are allowed to breed has resulted in the removal of alleles that produce undesireable traits from the gene pool and increased the frequency of alleles that produced desireable traits.
-Dog breeds have been subjected to intensive selective breeding programs
-This has occurred in a very short time space
Eg. Since 1860 bulldogs’ heads and faces have changed enormously and today’s animals have many health problems including breathing difficulties due to their short muzzles.