TYPES OF NATURAL SELECTION

Directional Selection Stabilizing Selection Disruptive Selection

DEFINE IN YOUR NOTES

A form of natural selection; occurs when individuals at one end of the distribution curve have higher fitness than individuals in the middle or at the other end of the curve. One EXTREME is favored.

DIRECTIONAL SELECTION

Example: Giraffes Selection for a long neck

DIRECTIONAL SELECTION

A form of natural selection; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end. EXTREMES are NOT selected AVERAGE is better.

STABILIZING SELECTION

STABILIZING SELECTION

Example: Human infant birth weight—it is a disadvantage to be really small or really big, and it is best to be somewhere in between.

STABILIZING SELECTION

A form of natural selection; occurs when two individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle. BOTH EXTREMES are selected for.

DISRUPTIVE SELECTION

DARWINS FINCHES

DISRUPTIVE SELECTION

WORD ASSOCIATIONS

Directional = 1 extreme Stabilizing = Average Disruptive = 2 extremes

Structure's that evolve because of the same environmental pressures.

For example, Birds and Bats. They do not have a recent common ancestor, but have managed to both evolve wings.

ANALOGOUS STRUCTURES

THE FOUNDER EFFECT

The loss of genetic variation when a new colony is formed by a very small number of individuals.

(This is why incest is not good) http:/ /

www.dnalc.org/view/15184-Mitochondrial -DNA-and-the-founder-eff ect-Douglas-Wal lace.html

ISOLATING MECHANISMS

When a new species evolves it’s because a population has become reproductively separated.

REPRODUCTIVE ISOLATION THERE’S 3 TYPES

When members of 2 populations cannot interbreed and make fertile offspring.

This is why we will never have a real life

CatDog.

Different species CANNOT combine and

reproduce.

BEHAVIORAL ISOLATION

This is when the same species are CAPABLE of reproducing but DON’T because they have different mating rituals.

Like a lion and a cheetah. BOTH are felines (cats) BUT they DON’T mate with each other.

GEOGRAPHIC ISOLATION

When species are separated by a geographic barrier, like an ocean, river or mountains.

Like a Brown Bear and a Polar Bear They are BOTH bearsBUT they are geographically separated so they can’t mate.

TEMPORAL ISOLATION

When species reproduce at different times.

For example, these 2 different types of frogsBOTH are frogs BUT one mates in the spring, while the other mates in the fall

ISOLATING MECHANISMS

Each of these could lead to the development of a new species.

https://www.youtube.com/watch?v=2oKlKmrbLoU