Mechanisms of Evolution Notes

Gene pool: The different alleles present in a population.
Allele frequency: The number of times an allele occurs in the gene pool.
Gene flow: (Not explicitly defined in the provided slides, but implied as a mechanism of evolution).
Genetic drift: Changes in allele frequency due to chance.
Bottleneck effect: Occurs when most of a population is destroyed.
Founder effect: Occurs when a small group of individuals is separated from the rest of the population to colonize a new area.

Population: A group of organisms that interbreed in a given location at a given time.
Each population shares a gene pool, which represents the different alleles present in the population.
Each population has a relative allele frequency, representing the number of times the allele occurs in the gene pool.
The frequency of alleles in a population tends not to change unless there is an outside force causing the change.

Shows an arrangement of data in which most of the values fall in the middle of the data set.
It is a bell-shaped curve.
Frequency is highest near the mean value.
Decreases toward each extreme end of the range.

Hypothetical scenario: If increasing temperatures select against a thick layer of fat and select for a thinner layer of fat, the normal distribution graph would be affected.

Occurs when individuals with the average form of a trait are most fit for the environment, and extreme traits could be eliminated over time.
This is the most common form of natural selection.

Occurs when individuals with one extreme variation of a trait are the most fit in the environment.
This causes a gradual shift in allele frequency to that extreme (shift in one “direction”).

Selection against one extreme.
For: one extreme trait.
Against: the other extreme.
Example: Long wiggly tails look like a snake and scare predators. The longer the tail, the more it looks like a snake.

Selection against both extremes.
For: moderate traits.
Against: both extremes.
Example: Short tails mess up the cat's balance. Long tails drag on the ground. Medium tails are best.

Selection against the mean.
For: both extremes.
Against: moderate traits.
Example: Short tails help keep predators from catching you on the ground. Long tails are good for balance in the trees. Medium tails don't help.

Genetic drift describes changes in allele frequency due to chance.
Example: natural disasters.
Allele frequencies can change more rapidly in smaller populations.
Smaller populations have less variation and, therefore, a lower ability to respond favorably to changing conditions.

The bottleneck effect occurs when most of the population is destroyed.
Example: Northern elephant seals were severely over hunted for their blubber (used in lamp oil). In 1890 there were less than 100 left. The population is now over 100,000 because of the restriction on hunting.

A founder event occurs when a small group of individuals is separated from the rest of the population.
A small number of individuals become isolated from the original population and colonize a new area.
Ex: Amish community.