LESSON # 22

1- An Introduction to Evolution

2- The Means of Evolution: Microevolution

A change of allele frequencies in a population over a relatively short period of time.

Any genetically based phenotype change in a population of organisms over successive generations.

Microevolution:

Evolution:

Macroevolution:Evolution that results in the formation of new species.

Evolution and Its Core Principles:

1- Common Descent with Modification

2- Natural Selection

Particular groups of species can undergo modifications in successive generations, sometimes resulting in the formation of new species.

1- Common Descent with Modification

The adaptation of organisms to their environment selects those traits that will be passed on with greater frequency from one generation to the next.

EXAMPLE

Honeybee with more sensitive eyesight have more possibilities to find food and survive. In this way, the trait of sensitive eyesight is being selected for transmission to a greater proportion of the population

2- Natural Selection

The Evidence for Evolution

1- Radiometric Dating

2- Fossils

3- Comparative Morphology and Embryology

4- Evidence for Gene Modification

5- Experimental Evidence

1- Radiometric DatingEvolution proceeds at a very slow pace, with billions of years between the appearance of life and the present. A technique is necessary to determine the age of the Earth and its organisms.

Radiometric Dating is a technique to determine the age of objects measuring the decay of the radioactive elements they contain.

Uranium 238 Lead 2064.5 billions of years

1/2

Comparing the proportion of parent element in the object (ex: a rock) with the proportion of the daughter element is possible to measure the age of the object

2- FossilsA general movement toward more complex organisms has been found as the scientists go up through a newer strata of the sedimentary layers of Earth.

Trilobites became extinct long before the primates came to exist. Never has been found fossils of trilobites with those of early primates in the same fossil bed.

3- Comparative Morphology and Embryology

Morphology: The study of the physical forms that organisms take.Diverse group of mammals, which descend from a common ancestor, has homologous features.

Embryology: The study of how animals develop from fertilization to birth.

At a certain point in their embryonic development, species as diverse as fish, chicken, cat, and human have similar structures known as pharyngeal slits.

4- Evidence for Gene Modification

1- The same genetic code is used for every living thing on Earth: a triplet of DNA specifies one aminoacid.

2- The longer it has been since any two species shared a common ancestor, the greater the number of base differences in their sequences of DNA.

5- Experimental Evidence Male guppies who are larger and have brighter coloration are chosen more often by females for mating. But they are also more visible for predators.Predator free environment:In only a few generations, the males evolved brighter coloration and larger tails.

When predators were reintroduced in the environment:Over several generations, the males evolved smaller tails and less brilliant colors.

2- The Means of Evolution:

Microevolution

A change of allele frequencies in a population over a relatively short period of time. No new species are originated.

EVOLUTION

Any genetically based phenotype change in a population of organisms over successive

generations.

Evolution that results in the formation of new species.

MICROEVOLUTION MACROEVOLUTION

All the alleles that exist in a population.

Gene Pool:a1 : dark coloration

a3 : light coloration 1

a4 : light coloration 2

a1(dark color)

a4 (light color)

MICRO-EVOLUTION

High frequency

Low frequency

a4 (light color) Low frequency

a1(dark color) High frequency

Species: A group of organisms who can successfully interbreed with one another in nature, but who don’t successfully interbreed with members of other such groups.

Biological species concept is based in the breeding behavior of populations.

Endangered species Not endangered

All the members of a single species that live in a defined geographic region.

Populations are the essential units that evolve.

Population:

(years of drought)

One species, two populations in two different environments: different predators, different vegetation.

Some individuals will be more successful than other in surviving and hence reproducing.

After many generations, coloration diverges as they adapt to the new environment pressures.

What has evolved is a population.

Gene pool: All the alleles that exist in a population.

Frequency of allele a1 has increased in the population:Microevolution.

a1:dark colorationLow frequency

a1:dark colorationHigh frequency

Evolution works with the gene pool.

What is That Evolves?

Populations Are the Essential Units That Evolve

Five Agents of Microevolution

1- Mutations

2- Gene flow

3- Genetic drift

4- Nonrandom mating

5- Natural selection

1-Mutation: Alterations in the Makeup of DNA

A change in a whole chromosome or part of it

A change in a single base pair in the DNA

- Inversion &

-Point mutation:

- Deletion

- Duplication

translocation

Mutations

Most do nothing

Many are harmful

Few are beneficial or adaptive

Importance of Adaptive Mutations

They are the only means by which NEW genetic information comes into being – by which new proteins are produced that can modified the form or capabilities of an organism.

2- Gene FlowThe movement of genes from one population to another during migration (the movement of individuals from one population into the territory of another).

Hawaiian silverswords are derived from Californian tarweeds

1- Human activity

2- Wind currents

3- Water currents

4- Animal dispersal of seed and pollen

3- Genetic DriftThe chance alteration of allele frequencies in a population, with such alterations having the greatest impact on small populations.

4- Nonrandom MatingWhen a given member of a population is not equally likely to mate with any other given member.Ex: If one male mates four times as much as the average male of his generation, the frequency of his alleles will increase in the next generation.

5- Natural Selection

It is a process in which the differential adaptation of organisms to their environment select those traits that will be passed on with greater frequency from one generation to the next.

Natural selection is the only agent of microevolution that consistently work to adapt organisms to their environment.

Therefore, it is considered the most important agent in having shaped the natural world.

DROUGHT

Only the birds with larger beaks survived.

(6% larger)