Microevolution

Question 1

Microevolution

Answer 1

Small-scale variation of allele frequencies within a species or population, in which the descendant is of the same taxonomic group as the ancestor

Question 2

Selection Pressure

Answer 2

An external (eg. environmental) factor that acts on a population of organisms. A selection pressure may be a biotic factor (caused by a living thing), such as predation, disease or competition, or an abiotic factor (non-living or physical), such as temperature, water, soil nutrients or fire.

Question 3

Natural Selection

Answer 3

Natural selection results in a change in the frequency of particular alleles within of a population over many generations due to action of a particular selection pressure which confers a selective advantage on a specific phenotype which then enhances that phenotypes (organism’s) survival and reproduction.

Question 4

5 Key Premises of Natural Selection

Answer 4

Overproduction – more offspring are produced than can survive to reproductive maturity.

Variation – populations contain variety (Variation is enhanced in populations via sexual reproduction and mutations)

Competition – is the struggle between organisms for the same resources (such as food, shelter and mates).

Survival of the fittest – those individuals with the most ‘favourable’ genetic variations survive better (good viability) and then reproduce (good fecundity) and then pass on their genes / alleles to the next generation.

Combinations of ‘favourable’ variations / characteristics increase in frequency in the population.

Question 5

Types of phenotypic selection

Answer 5

Positive selection is selection that favours a heritable trait (ie allele frequency for that trait will increase)

Negative selection is selection does not favour a heritable trait (ie allele frequency for that trait will decrease)

Question 6

Main modes of phenotypic selection

Answer 6

Stabilising selection: where a selection pressure favours an intermediate phenotype on the spectrum (acts against extreme forms of a trait)

Directional selection: where a selection pressure favours one end of the phenotype spectrum (shifting allele frequency towards the left or right)

Disruptive (or Diversifying) selection: where a selection pressure favours each end of the phenotype spectrum (favours extreme forms of the trait)