Evolution | Genetics and Evolution - Biology IB23

Evolution

The change in heritable characteristics over several generations.

Natural Selection

1. Variation

2. Overproduction

3. Competition

4. Adaptation

5. Heritage

6. Change

Variation

Variations can be caused by:

1. Mutations in DNA

   a) Mutations can be random

   b) Mutations can be caused by exposure to radiation, chemicals or viruses.

2. Sexual Reproduction from a mix of DNA during meiosis.

Overproduction

An overproduction of young means the environment can’t sustain well since there’s a carrying capacity of the environment, which limits how many organisms in a population can be supported.

Competition

As a consequence of overproduction, competition occurs between individuals of the same species for resources such as food, shelter, mates and predator avoidance.

Adaptation

Individuals who have best adapted genetics for their surrounding environment will survive better and reproduce more. Survival of the fittest.

Heritage

Characteristics adapted to their environment will be passed down to offspring.

Change

Over many generations, characteristics of a population will change which is what defines evolution.

Stabilizing Selection

Rejects extreme variations.

1. Baby sizes can’t be too small or they’ll die, but they can’t be too big either and the mother dies as a result.

2. Robin birds laying clutches of eggs usually comes in 4, too many eggs leads to malnourished chicks while too few eggs can result in no viable offspring.

Directional Selection

Favours one extreme variation.

1. Cows have been bred to produce larger quantities of milk over the years by selecting the best cows to breed. Cows that do not produce as much milk aren’t allowed to breed.

2. Teosinte, original corn plants, have been made bigger through selective breeding.

Disruptive Selection

Favours both extreme variations.

1. Squirrels either have a long tail for better balance when climbing trees, or very short tails so predators have difficulty catching them.