Industrial Melanism and Microevolution

Hierarchical Classification

Gene Flow additions to and/or subtractions from a population resulting in the movement of fertile individuals or gametes

Gene Flow and Human Evolution Increasing migra- tion of people throughout the world has contributed to an increase in gene flow

Mutation and Sexual Recombination produce 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 subgroup of 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: 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 the toes!

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

Cepaea Snails Disruptive Selection

(3) Disruptive Selection The curve has two peaks; dark shells appear in most forested areas whereas light-banded shells appear in areas of low lying vegetation Ex – 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 Fashion Perfect Organisms 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 the distribution of phenotypes in three ways. They are: _______________ selection and _______________ selection.

A small population of organisms is suddenly cut off from the others in the population. This is known as the _____________ effect. A small group of organisms migrates from one area to another. There is not a wide variation in the gene pool. This is known as the ___________ effect.