TYPES OF NATURAL SELECTION. DEFINITIONS.. Evolution is the change in a population’s genetic...

TYPES OF NATURAL SELECTION

DEFINITIONS..

• Evolution is the change in a population’s genetic material (alleles) over generations.

DEFINITIONS..


• A population is in genetic equilibrium if it’s not evolving

DEFINITIONS..


• A population is in genetic equilibrium if it’s not evolving.

• If the population’s allele frequencies stay the same year to year then it’s not evolving.

HARDY-WEINBERG GENETIC EQUILIBRIUM• Hardy-Weinberg equilibrium describes

populations that are not evolving



• Genotype frequencies stay the same over time as long as certain conditions are met:



• Genotype frequencies stay the same over time as long as certain conditions are met:

• Very large populations

• No emigration or immigration

• No mutations

• Random mating

• No natural selection

NATURAL SELECTION (3 TYPES) • Organisms best suited to their environment live

to reproduce and pass on their genes

• Acts on a phenotype

• Varying types of selection

1. DIRECTIONAL SELECTION

• Individuals with a more extreme form of trait have higher fitness

Normal DistributionDistribution after Selection

Suppose termites in an area begin to build deeper nests. Anteaters with long tongues could more effectively prey on termites than those with short or average tongue length

2. STABILIZING SELECTION

• Having average form of trait has highest fitness


Blue curve shoes variation after a new predator is introduced. Predator can easilty capture the large, visible lizards and the small slower lizards. Thus, selection against these extremes body types reduces the size range in lizards

3. DISRUPTIVE SELECTION

• Individuals with any extreme trait has a higher fitness and most likely results in two new species

• Divergent Evolution


The white limpets blend in with barnacles on rocks. On bare rocks, dark-shelled limpets blend in. However, the tan colored limpets are easy to spot by birds.

TYPES OF NATURAL SELECTION. DEFINITIONS.. Evolution is the change in a population’s genetic...

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