Evolution Notes

Charles Darwin –"On the origin of Species"

Populations evolve; Individuals don’t! The entire collection of genes among a population is its gene pool.

Population evolve; Individuals don’t! The allelic frequency is the percentage of a particular allele in the gene pool.

Genetic equilibrium occurs when the frequency of alleles does not change from generation to generation. Population evolve; Individuals don’t! Second GenerationThird Generation

Evolution can only occur when genetic equilibrium is disrupted. Population evolve; Individuals don’t!

Mechanisms for disruption in genetic equilibrium Mutations –Result in genetic changes to a gene pool –Most mutations are harmful and, therefore, selected against. –Some are favorable and become part of future generations.

Mechanisms for disruption in genetic equilibrium Genetic Drift –The alteration of allelic frequencies by chance processes. –More common in small populations than large ones. –In small populations, it is much more likely that recessive traits will be passed on.

Movement of individuals in and out of a population. –When an individual enters, genes are added to the gene pool. –When an individual leaves, genes are lost to the gene pool. Mechanisms for disruption in genetic equilibrium

Natural Selection –The most significant factor that alters genetic equilibrium and causes changes in the gene pool. Mechanisms for disruption in genetic equilibrium “Survival of the fittest”

Types of Natural Selection Stabilizing selection –Favors average individuals in a population

Directional selection –When one of the extreme forms of the trait is favored by natural selection. Types of Natural Selection

Disruptive selection –Both extremes of the trait are favored by natural selection. –Eliminates average forms Types of Natural Selection

Significant changes in the gene pool can lead to the formation of a new species.

Speciation is when a new species evolves. Can occur only when either interbreeding or the production of fertile offspring is prevented.

Physical Barriers –Can prevent interbreeding. –When a barrier forms that breaks up large populations into smaller ones. Speciation is when a new species evolves.

Geographic isolation is when a physical barrier separates a population into groups. –Can be anything from a river to a mountain range. –Over time, the small population adapts to the local environment and through the process of natural selection, could become a new species. –Can lead to differences in mating behavior. Speciation is when a new species evolves.

Hyla versicolor Hyla chrysocelis

Reproductive Isolation can occur when formerly interbreeding organisms are prevented from producing fertile offspring. –Sometimes the two species become so different that mistakes happen in the formation of the zygote, preventing fertility. –Seasonal problems happen when the two species mate at different times of the year. Speciation is when a new species evolves.

Polyploid speciation is when a species has multiples of the normal set of chromosomes.Polyploid speciation is when a species has multiples of the normal set of chromosomes. –Happens because of mistakes in meiosis. –Fastest form of speciation because it causes reproductive isolation instantly. –Nearly half of known flowering plant species originated in this way, as well as many important crops. Speciation can occur when chromosome numbers change.

Gradualism is the idea that species originate through a gradual buildup of new adaptations.

Punctuated equilibrium is the idea that speciation occurs quickly in rapid bursts with long periods of stability in between.

Both gradualism and punctuated equilibrium theories are supported by the fossil record.

Patterns of Evolution Adaptive radiation is the process of evolution of an ancestral species into an array of species that occupy different niches. –Darwin’s Finches are an example of adaptive radiation. Each finch adapted to its particular environment on different islands.

Adaptive Radiation – Darwin’s Finches

Divergent Evolution is when species that were all similar to the ancestral species become more and more distinct. –Occurs when species begin to adapt to different environmental conditions and change according to natural selection. Patterns of Evolution Homologous Structures Homologous Structures: Same Structure; Different Function

Embryology

Convergent Evolution is when distantly related organisms evolve similar traits. –Occurs when unrelated organisms occupy similar environments and face similar pressures. Patterns of Evolution Analogous Structures: Analogous Structures: Same Function; Different Structure

Evidence for Evolution A.Homologous Structures -Modified structure that is seen among different groups -Similar in structure NOT function -Example: arms, wings and flippers -Used to indicate evolutionary relationships

B. Analagous Structures -Any body part that is similar in function, but different in structure -Example: wings of butterfly and bat -Can NOT be used to indicate evolutionary relationships

C. Vestigial Structures -Body structure that is reduced in function in a living organism but may have been used in an ancestor -Example: appendix -Claws on snakes

Hip bones on a whale?

II. Historical Evidence The earth is thought to have formed about 4.6 billion years ago. A. Fossils are the preserved remains of ancient organisms

1.Mold- empty space in rock showing the exact shape of the organism that was buried and decayed there.

2. Cast – Object formed when a mold is filled in by minerals from the surrounding rock

3. Petrified fossils – exact stone copy of an original organism, the hard parts of which have been penetrated and replaced by minerals

4. Imprints – thin objects, such as leaves or feathers that fell into sediments and formed fossils before the sediment hardened

5. Amber - fossil embedded in tree sap, valuable because the organism is preserved intact.

Paleontologist scientist who specialize in the study of fossils 1. Relative dating – determining the age of fossils by their position in sedimentary rock

FOSSIL RECORD 1. The fossil record indicates what animals lived in the past and gives us a clue as to their behavior

Relative Dating The older fossils are found on the bottom and as you move up through the layer soft rock the fossils become more recent Gives us a time scale

2. Carbon dating- determining the age of a fossil based on its half life.

Evidences for Evolution 1. Fossil Record 2. Vestigial Structures 3. Embryology - embryos of animals are nearly identical 4. Homologous Structures