Industrial Melanism and Microevolution

Microevolution of the fruit fly (Drosophila) species on the Hawaiian archipelago

Hierarchical Classification

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

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

Out of Africa Likely migration paths of humans out of Africa 10-20,000ya 10-20,000ya Migration Paths According to the "Out of Africa" theory, modern humans appeared as a single African species nearly 100,000 years ago, then spread throughout the world (K.Wong, Is Out of Africa Going Out the Door?, Scientific American 281(2), August 1999). 50,000ya Many patterns of human traits reflect this migration

Variation & Natural Selection Variation is the raw material for natural selection there have to be differences within population some individuals must be more fit than others

Five Agents of Evolutionary Change Mutation Gene Flow Non-random mating Genetic Drift Selection

Not every mutation has a visible effect. Mutation & Variation Mutation creates variation new mutations are constantly appearing Mutation changes DNA sequence changes amino acid sequence changes protein’s: Structure function changes in protein may change phenotype & therefore change fitness Every individual has hundreds of mutations 1 in 100,000 bases copied 3 billion bases in human genome But most happen in introns, spacers, junk of various kind Not every mutation has a visible effect. Some effects on subtle. May just affect rate of expression of a gene.

Gene Flow Movement of individuals & alleles in & out of populations seed & pollen distribution by wind & insect migration of animals sub-populations may have different allele frequencies causes genetic mixing across regions reduce differences between populations

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

Bottleneck Effect When large population is drastically reduced by a disaster famine, natural disaster, loss of habitat… loss of variation by chance event alleles lost from gene pool not due to fitness narrows the gene pool

Cheetahs All cheetahs share a small number of alleles 2 bottlenecks less than 1% diversity as if all cheetahs are identical twins 2 bottlenecks 10,000 years ago Ice Age last 100 years poaching & loss of habitat

Northern Elephant Seals Hunted to nearly extinction in the late 1800s for their oil.

Founder Effect: Polydactylism in the Amish Population migration of a small subgroup of the population; a type of genetic drift

Amish Country: Lancaster County, Pennsylvania

One Room Schoolhouse -Amish Country: Lancaster County, PA

Founder Effect in Amish Ellis-van Creveld Syndrome Causes dwarfism and polydactyly

Founder Effect When a new population is started by only a few individuals some rare alleles may be at high frequency; others may be missing skew the gene pool of new population human populations that started from small group of colonists Small founder group, less genetic diversity than Africans All white people around the world are descended from a small group of ancestors 100,000 years ago (Chinese are white people!)

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

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

Stabilizing Selection

Cepaea Snails Disruptive Selection

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

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

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.

Types of Selection (2) Stabilizing Selection Ex - when human babies with low or high birth weight are less likely to survive