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Why is Natural variation so important?

So disease will not wipe out a population.

Selective Breeding

Choosing characters in offspring.


Blending mixing or breeding 2 organisms.
-Ex: If you want a really healthy dog, breed a mutt, not a purebred.

How can inbreeding cause health problems?

Purebreds share similar genetic make-up.

2 Causes of Gene Shuffling.

1-Chromosomes of homologous pairs move independently during meiosis.
2-Crossing over further increases number of different genotypes.

Do Mutations cause serious health problems?


2 diseases caused by minor mutations.

1-Sickle-cell anemia
2-cystic fibrosis.

Gene Pool

All genes and their different alleles in a population.

Relative frequency.

The number of times that allele occurs in the gene pool, compared to the number of times all other alleles for that same gene occur.

Monogenic Traits

Single gene trait.
-Bar graph

Polygenic traits

-bell curve
-multigenic traits

Natural Selection

The process by which organisms with favorable variations reproduce at higher rates than those without such variations.

Stabilizing Selection

individuals with the average form of the trait has the highest fitness.

Directional Selection

individuals with the more extreme form of a trait have a higher fitness than individuals with an average form.

Disruptive Selection

individuals with either extreme variation of a trait have a higher fitness than those with the average form.

Survival of the Fittest

The more fit (adapted) the organism, the better chances they have to survive.

How do organism adapt to their environment?

Change food, grow hair, etc.

What causes adaptations?

Change of climate.

Genetic Drift

the gradual changes in gene frequencies in a population due to random events

By what means does genetic drift occur?


The Founder Effect

when few individuals begin a new isolated population

Why does the Founder's Effect occur most likely after a Natural Disaster?

The organisms could be seperated by the natural disaster, forcing the animals to adapt to their new environment.

Hardy-Weinberg Principle

Allele frequencies remain constant unless there are 1 or more factors.

5 conditions to maintain genetic equilbrium.

1-Random mating
2-Very large population
3-no immigration or emmigration
4-No mutations
5-No Natural Selection


The formation of a new species

3 types of reproductive isolation


Behavioral Isolation

2 populations are capable of interbreeding but do not understand each others courtship rituals.

Geographic Isolation

Geographic barriers seperate populations.

Temporal Isolation

2 or more species reproduce at different times.

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