BIOL 2390 - Topic 5 (part 3)

Genetic drift

Random fluctuations in allele frequencies, usually when genes are lost in a population, due to the random nature of sexual reproduction

Example of genetic drift

Some individuals are not able to find a mate, despite their high reproductive rate, meaning that they cannot pass on their favourable genes, resulting in a simplified population

Occurrence of genetic drift

1.) It is mainly seen in small populations

2.) It is commonly observed in new colonizations or after population crashes

Genetic drift act like…

It acts like a sampling error, due to each generation only representing a small subset of the gene pool

Negative consequences of genetic drift

It reduces genetic diversity, resulting in increased extinction risk

Why does genetic drift increase extinction risk?

1.) Genetic drift causes reduced genetic diversity, resulting in a simplified population

2.) Therefore, when they respond to a something, it is all uniform and there is no variation, therefore they are all likely to die

Gene flow

Refers to when individuals switch back and forth between subpopulations and even metapopulations, specifically when they reproduce in different sub/meta-populations

Significance of gene flow

It acts as a strong force that reduces genetic differences between subpopulations, preventing them from diverging too much from each other

What happens when gene flow stops

Since traits are no longer being shared between the subpopulations, it causes them to drift apart and may even eventually cause speciation

Non-random mating

1.) When individuals select mates based on specific phenotypic traits, therefore those that don’t have the trait are selected against

2.) It is aka sexual selection and is known to drive evolution

Genetic differentiation

Refers to species that have a wide range of environmental conditions/distributions and can therefore result in…

1.) Clines

2.) Ecotypes

3.) Geographic isolates

Clines

1.) It describes gradual, measurable changes in a phenotypic trait across a geographic area

2.) It is often correlated with environmental gradients, such that the trait changes as environmental conditions change over a region

Clines environmental gradients examples

1.) Temperature

2.) Moisture

3.) Altitude

Clines example

1.) Deer gets heavier as they enter colder climates

2.) This is because the bigger their bodies, the better they are able to conserve heat

Ecotypes

Refers to species with an abrupt and dramatic difference in characters, usually well adapted towards the local environment they are in

Do ecotypes have a gradual transitional gradient?

No

Ecotypes example

1.) Lions in Savannah grasslands have very thick mane

2.) Lions in shrublands barely have any mane and this is because it would likely get tangled while they are running through the shrubs

Geographic isolates

1.) Refers to populations of species that are separated by extrinsic barriers that prevents movement between the different subpopulations, therefore limiting gene flow

2.) How isolated they are from one another depends on the efficiency of the barrier

Consequences of geographic isolates

Over time, the geographic isolation can lead to more and more genetic divergence, until speciation eventually occurs because they no longer have any shared traits

Gene flow in clines and ecotypes vs. geographic isolates

In clines and ecotypes, gene flow still occurs, but gene flow in geographic isolates is very restricted

Complete isolation in geographic isolates

It is rare?

Geographic isolates example

Salamanders

Sub-species

1.) Term used when very little gene flow exists between populations, based on having 1 or more differences in major characteristics

2.) It does not only apply to geographic isolates, but ecotypes too