3. Speciation and genetic Drift

speciation

the formation of new species due to selective pressures.

microevolution

changes in the gene frequency and phenotypic traits within a population.

Allopatric speciation

When a population is split by a geographical barrier such as a river or mountain range, preventing interbreeding between the two populations of the species.

Sympatric speciation

Formation of new species from one ancestral species without any geographical separation.

List and briefly describe all 3 mechanisms of reproductive isolation - Sympatric speciation

Seasonal changes - individuals develop different flowering/ mating seasons/ become sexually active at different times of the year.

Mechanical changes - Changes in size, shape or function of genitalia can prevent successful mating, preventing individuals from breeding.

Behavioural changes - group of individuals may for an example develop courtship rituals that aren’t attractive to the rest of the species, such as a song for birds. Can prevent breeding, even if they could do it successfully.

Genetic drift

The random drift between phenotypes that can occur in a population.

2 types of genetic drift

founder effect

bottlenecking

founder effect

The genetics of the population reflect those of the initial members.

bottlenecking

a portion of the population is randomly eliminated resulting in a population that reflects the genetics of the survivors.

describe the bottleneck

• sharp reduction of population size

• Caused by environmental events, human activities

• Produces small population with reduced genetic diversity.

• Remains lower, only increasing with time as random mutations occur.