Industrial Melanism and Microevolution

Hierarchical Classification

Gene Flowadditions to and/or subtractions froma population resulting in the movementof fertile individuals or gametes

Gene Flow and Human Evolution

Increasing migra-tion of people throughout the world has contributedto an increase ingene flow

Mutation and Sexual Recombinationproduce the variation that makes evolution possible

Genetic Drift occurs by chance when only certain members of a population reproduce and pass on their genes

Genetic Drift

Bottleneck Effect: a sudden change in the environment drastically

reduces the size of the population

Cheetah

Northern Elephant Seals

Founder Effect:

Polydactylism in the Amish Population

migration of a small subgroupof the population

Founder Effect in Amish

Ellis-van Creveld Syndrome

Causes dwarfism and polydactyly

The evolution of fruit fly (Drosophila) species on the Hawaiian archipelago (Founder Effect)

• Natural Selection is the primary mechanism of adaptive evolution

• Out of all the factors that can affect a gene pool only natural selection is likely to adapt a population to its environment

Mapping Malaria and the Sickle-Cell Allele

This is a good example of heterozygote advantage.

Modes of Selection

Types of Selection• Most traits are polygenic - variations in the

trait result in a bell-shaped curve

• Three types of selection occur:

1) Directional Selection – the curve shifts in one direction ex: resistance to antibiotics by bacteria

Directional Selection

Evolution of the Horse over 50 million yrs

Hyracotherium

American Museum of Natural History

Orohippus

Note thetoes!

Directional selection for beak size in a Galápagos

population of the medium ground finch

Types of Selection

–(2) Stabilizing Selection

•Ex - when human babies with low or high birth weight are less likely to survive

Stabilizing Selection

Disruptive SelectionCepaeaSnails

(3) Disruptive SelectionThe curve has two peaks; dark shellsappear in most forested areas whereas light-banded shells appear in areas of low lying vegetationEx – When Cepaea snails vary because a wide geographic range causes selection to vary

Disruptive or Diversifying Selection

Small-billed birds feed on soft seeds; large-billed birds feed on hard seeds (Black-bellied Seed Crackers – Cameroon, Africa)

The Two-Fold Disadvantage of Sex

Why Natural Selection Cannot FashionPerfect Organisms

1) Evolution is limited by historical constraints.

2) Adaptations are often compromises.

3) Chance and natural selection interact.

4) Selection can only edit existing variations.

Natural selection can affect thedistribution of phenotypes in three ways. They are:_______________ selection_______________ selectionand _______________ selection.

A small population of organisms issuddenly cut off from the others

in the population. This is known asthe _____________ effect.

A small group of organisms migrates from one area to another. There is not a widevariation in the gene pool. This is knownas the ___________ effect.