Unit 10 - Genetics and Evolution

Question 1

Define gene pool

Answer 1

The sum total of alleles for all genes present in a sexually reproducing poluation

Question 1

Explain the mechanisms whereby a large population turns into a small population

Answer 1

Population bottlenecks:
This event occurs when a population is minimised to less than 50% and can occur from natural occurrences like a forest fire or from human induced factors like poaching. The surviving population has less genetic variability and will, thus, be subject to greater levels of genetic drift. Only certain alleles of the prior population will survive in the new population.

Founder effect:
This occurs when a small group breaks away from a larger population to colonise a new territory. As the moved population has a smaller gene pool there will be more genetic drift. This is different due to the fact the prior population will, most likely, remain intact.

Question 2

Explain the types of selection

Answer 2

Stabilising selection:
Removes the extremes of a population, i.e. a gradient from black to white. The extremes, black and white will disappear, leaving only grey.

Directional selection:
Favours one of the extremes, following the same example would leave only black or only white species.

Disruptive selection:
Favours both extremes, so only black and white for example, and creates a bimodal distribution

Question 3

Explain the three isolation barriers

Answer 3

Temporal isolation
One organism reaches sexual maturity before the other; they cannot interbreed to produce offspring.

Behavioural isolation
One organism only responds to a specific mating call that can’t be recreated by another organism; they will not interbreed (usually).

Geographical isolation
A barrier, like a mountain or valley, between a species removes the possibility of them interbreeding so they will not create fertile offspring.

Question 4

Explain the two types of speciation

Answer 4

Allopatric speciation is the formation of new species in two different areas that are seperated by a geographical barrier. This is due to the fact that the two groups evolve in different ways as a result of mutation, genetic drift and natural selection.

Sympatric speciation is the divergence of species within the same geographic location. This may occur from the reproductive isolation of two species as a result of genetic abnormalities. Usually, a chromosomal error may arise which prevents successful reproducing with organisms that don’t pertain the same characteristic. This abnormality is usually polyploidy which is an error that occurs in cytokinesis. Fe