Mutation & genetic drift
Transcript of Mutation & genetic drift
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
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
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
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
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)