Mutation Genetic Drift o Natural Selectiono Gene Flow

Speciation: the process by which populations become different species

Microevolution: results from evolutionary mechanisms (mutation, drift, selection, etc) acting within a population

Macroevolution: refers to evolutionary change above the species level

MUTATION Any heritable change in the DNA of a cell or an

alteration in a DNA sequence

Main features of molecular mutation:• Germ line mutation – Affects tissues that produces the sperm and egg

• Somatic mutation – Affects other body tissues (e.g. cancer)

• Errors during cell division brought about by endogenous or exogenous factors

• Mutation happens at random – whether a particular mutation happens or not is unrelated to how useful that mutation would be

• The ultimate source of all genetic variation

Existing variation can be reshuffled by a variety of mechanisms that we don’t always consider as mutations leading to increases or decreases in variation and thus altering the potential for evolution

MUTATION

MUTATION

GENETIC DRIFT

GENETIC DRIFT

First introduced by Sewall Wright

Changes in allele frequencies from one generation to the next that occurs by chance events

Loss in genes to a small population means that certain combinations cannot arise and will never be tested by natural selection. Overtime, the small population of flowers will be Red=1.0 and white=0.0

GENETIC DRIFT

Small populations are much more likely to experience genetic drift than large populations. Why?

Genetic drift may cause gene variants to disappear completely and thereby reduce genetic variation

GENETIC DRIFT

Fixation in the “blue allele” within five generations

Reduced genetic variation

The Bottleneck Effect- A bottleneck event (e.g. earthquakes,

fires, over-hunting) decimates a population and results in only a small number of individuals surviving

- the remaining, random survivors may not have the same allele and genotype frequencies as the original population

Population bottleneck

Gypaetus barbatus

As a consequence, the loss of variation leaves the surviving population vulnerable to any new selection pressures such as disease, climate change, or shift in the available food source, because adapting in response to environmental changes requires sufficient genetic variation in the population for natural selection to take place…

The Founder Effect Occurs when a few individuals representing a

fraction of the original allele pool, invade a new area and establish a new population

there is isolation from the original population which prevents breeding between the two populations

By random chance alone, the allelic frequencies of one or more genes in the new population can be quite different than those of the original population

Founder Population

Example:- Amish migration to Pennsylvania – 1700s- Ellis-van Creveld syndrome (allele frequency is 7% = 0.1% in general population)

- Genetic isolation and group interbreeding allows the frequency of the allele for Ellis-van Creveld syndrome to not only persist but increase over time

Some errors during DNA production/copying become incorporated into gametes (mutation)

Loss of pollen through chance events (genetic drift)

Migration/Gene Flow

Loss of some seed through chance events (genetic drift)

Plants that are better adapted, survive, grow more quickly, and produce more young than others (Natural selection)