Origins of Life on Earth 4.7-4.8 Billion Year History Evidence from chemical analysis and measurements of radioactive elements in primitive rocks and fossils. Life developed over two main phases: Chemical evolution (took about 1 billion years) Organic molecules, proteins, polymers, and chemical reactions to form first “protocells” Biological evolution (3.7 billion years) From single celled prokaryotic bacteria to eukaryotic creatures to eukaryotic multicellular organisms (diversification of species)

Summary of Evolution of Life Formation of the earth’s early crust and atmosphere Small organic molecules form in the seas Large (biopolymers) First protocells Single-cell prokaryotes eukaryotes Variety of multicellular organisms form, first in the seas and later on land Chemical Evolution (1 billion years) Biological Evolution (3.7 billion years)

DNA The double-helix structure of DNA was discovered in 1953. This showed how genetic information is transferred from one cell to another almost without error. Presenter notes: The genotype of an organism is stored in DNA molecules, which are a sort of information bank found within the nucleus of every cell. Every time an organism grows a new cell a new copy of the DNA is created. It is important that every copy of the DNA is identical, since any errors copying the genotype may prevent the cell from functioning properly. In 1953, Watson and Crick figured out that DNA had a helical structure and showed how it copies itself with such amazing accuracy. When DNA replicates, the helix unwinds and each strand produces an exact mirror image copy of itself. This ensures that each copy is identical to the original. Watson and Crick and their model of DNA DNA replication www.chem.ucsb.edu/~kalju/chem110L/public/tutorial/images/WatsonCrick.jpg en.wikipedia.org/wiki/DNA

MUTATIONS Changes in the structure of the DNA Adds genetic diversity to the population May or may not be adaptive Depends on the environment!

Mutation Mutations are rare and often have damaging effects. Mutations may be caused by radiation, viruses, or carcinogens. However, occasional mutations or copying errors can and do occur when DNA is replicated. Consequently organisms have special enzymes whose job it is to repair faulty DNA. Mutant fruitfly Presenter notes: However, very occasionally, tiny copying errors can and do occur when DNA is replicated. These copying errors are called mutations. Mutations may be caused by a number of factors including radiation, viruses, or carcinogens (cancer-causing materials). As the genotype provides the blueprint for how each cell should grow and function, even a tiny mutation might mean that the cells fail to work properly. Take for example the common fruitfly: a single mutation in the fruitfly can change the colour of the eye from red (its normal colour) to white. White-eyed fruitfly are less successful at mating. Because of the potential for mutation, most organisms have a group of special enzymes whose job it is to go round and repair any faulty DNA.

Rates of mutation Measured by phenotypic effects in humans: Rate of 10-6 to 10-5 per gamete per generation Total number of genes? Estimates range from about 30,000 to over 100,000! Nearly everyone is a mutant!

Rates of mutation Mutation rate of the HIV–AIDS virus: One error every 104 to 105 base pairs Size of the HIV–AIDS genome: About 104 to 105 base pairs So, about one mutation per replication!

Rates of mutation Rates of mutation generally high Leads to a high load of deleterious (harmful) mutations

Types of mutations Point mutations Base-pair substitutions Caused by chance errors during synthesis or repair of DNA Leads to new alleles (may or may not change phenotypes)

Types of mutations Gene duplication Result of unequal crossing over during meiosis Leads to redundant genes Which may mutate freely And may thus gain new functions

Types of mutations Chromosome duplication Caused by errors in meiosis (mitosis in plants) Common in plants Leads to polyploidy Can lead to new species of plants Due to inability to interbreed

Transitions are more common than transversions because Figure 5.4 Transitions and transversions Transitions are more common than transversions because DNA repair enzymes can recognize wrong insertion representing a a transition better than a transversion

Variation Some mutations will persist and increase genetic variation within a population. Variants of a particular gene are known as alleles. For example, the one of the genes for hair colour comprises brown/blonde alleles. Presenter notes: Mutations give rise to variants, or alleles, of the same gene. One person may have one set of alleles, and another person, a different set. For example, take hair colour in humans. One of the genes that codes for hair colour occurs as two alleles, brown and blonde. If you throw you mind back to earlier in this talk you’ll remember how Mendel showed that one allele is usually dominant and the other recessive. In the case of hair colour, brown is dominant and blonde is recessive. So if a person gets a brown allele from one parent and a blonde allele from the other parent, they will have brown hair. A person will only have blonde hair where they receive blonde alleles from both parents.

Natural Selection Mutant alleles spread through a population by sexual reproduction. If an allele exerts a harmful effect, it will reduce the ability of the individual to reproduce and the allele will probably be removed from the population. In contrast, mutants with favorable effects are preferentially passed on Selection of dark gene Presenter notes: If a person, or any other organism for that matter, develops a new allele (a mutation), they can spread this around the population by sexual reproduction. However, if the allele exerts a harmful effect on the individual then this will reduce the likelihood of it reproducing and the allele will be removed from the population. Only those mutant alleles that have beneficial effects that increase the likelihood of reproduction will be passed on to offspring. In this way, harmful alleles are removed from a population while favorable alleles accumulate. This is Darwin’s concept of Natural Selection and shows how a population adapts to its environment over time. en.wikipedia.org/wiki/Image:Mutation_and_selection_diagram.svg

When faced with a change in environmental condition, a population of a species can get MAD: MIGRATE to a more favorable location ALREADY be adapted DIE Natural selection can only act on inherited alleles already present in the population.

Reproductive capacity may limit a population’s ability to adapt If you reproduce quickly (insects, bacteria) then your population can adapt to changes in a short time. If you reproduce slowly (elephants, tigers, corals) then it takes thousands or millions of years to adapt through natural selection

What’s Evolution? The change in a POPULATION’S genetic makeup (gene pool) over time (successive generations) Those with selective advantages (i.e., adaptations), survive and reproduce. All species descended from earlier ancestor species

4 major mechanisms that drive evolution: Natural Selection Mutation Gene Flow Genetic Drift

Three types of Natural Selection Directional Allele frequencies shift to favor individuals at one extreme of the normal range Only one side of the distribution reproduce Population looks different over time Stabilizing Favors individuals with an average genetic makeup Only the middle reproduce Population looks more similar over time (elim. extremes) Disruptive (aka Diversifying) Environmental conditions favor individuals at both ends of the genetic spectrum Population split into two groups

Microevolution Small genetic changes in a population such as the spread of a mutation or the change in the frequency of a single allele due to selection (changes to gene pool)

Four Processes cause Microevolution Mutation (random changes in DNA—ultimate source of new alleles) Exposure to mutagens or random mistakes in copying Random/unpredictable relatively rare Natural Selection (more fit = more offspring) Gene flow (movement of genes between pop’s) Genetic drift (change in gene pool due to random/chance events)

Ex: Peppered Moth   The Peppered Moth is an example of Natural Selection in action discovered by Haldane During the Industrial Revolution the trees on which the moth rested became soot-covered.   Presenter notes: The case of the Peppered Moth is an excellent example of Darwin’s Natural Selection in action put forward by the biologist J.B.S. Haldane in 1924. The gene that controls the colour of the Peppered Moth occurs as two alleles, a mottled allele (pale colour) and a melanic allele (black colour). Early in the 18th century, pale moths were dominant in the countryside around Manchester. However, during the Industrial Revolution the trees on which the moths rested became covered in black soot. Pale mottled moths were poorly camouflaged on the black tree trunks and were preferentially eaten by birds. In contrast, the black melanic moths were better at avoiding predation. Natural Selection acted against the pale moths and in only a few generations, the melanic moths were dominant. However, there was one final twist. As the skies of Manchester became cleaner in the 20th century, the mottled moths made a comeback and displaced the melanic moths again. This selected against the allele for pale colour in the population (which were poorly camouflaged from predators) and selected for the dark colour allele. http://en.wikipedia.org/wiki/Image:Biston.betularia.7200.jpg en.wikipedia.org/wiki/Image:Biston.betularia.f.carbonaria.7209.jpg en.wikipedia.org/wiki/J._B._S._Haldane

Microevolution The dog is another example of how selection can change the frequency of alleles in a population. Dogs have been artificially selected for certain characteristics for many years, and different breeds have different alleles. All breeds of dog belong to the same species, Canis lupus (the wolf) so this is an example of Microevolution as no new species has resulted. Presenter notes: The case of the Peppered Moth shows how natural selection can change the frequency (or relative proportion) of alleles in a population. A more straightforward example of the same phenomenon is the breeding of dogs. Humans have been breeding dogs for thousands of years and trying to develop certain characteristics. This “artificial selection” is exactly the same process as natural selection but controlled by human intention rather than natural forces. Although humans have been successful in changing the frequency of alleles in different dog breeds, they haven’t created new species. The definition of a species is a population that can interbreed and produce fertile offspring. Most dogs can successively interbreed with other dogs, and also with wolves, so in actual fact all dog breeds are just subspecies of the wolf, Canis lupus! Dog breeding is therefore an example of what biologists called Microevolution; the frequency of alleles in the population have changed, but not greatly enough to give rise to a new species. Dogs are wolves www.puppy-training-solutions.com/image-files/dog-breed-information.jpg

Macroevolution Long term, large scale evolutionary changes through which new species are formed and others are lost through extinction.

Macroevolution is the cumulative result of a series of microevolutionary events Typically seen in fossil record Nobody around to see the small, gene pool changes over time.

Macroevolution However, if two populations of a species become isolated from one another for tens of thousands of years, genetic difference may become marked. If the two populations can no-longer interbreed, new species are born. This is called Macroevolution. Darwin’s Galapagos finches are an example of this process in action. Galapagos finches Presenter notes: To give rise to a new species, Microevolution needs to go on for more much longer than humans have been breeding dogs. For example, if a species was to become divided into two isolated populations for tens of thousands of years, then natural selection would eventually change the frequency of alleles to such an extent that members of the two populations could no longer interbreed. This process would result in the birth of new species or speciation. Where speciation occurs, biologists refer to the process as Macroevolution. An excellent example of Macroevolution is that observed by Charles Darwin during his world tour on HMS Beagle. When visiting the Galapagos Islands in the Pacific Ocean he noticed that each island had its own distinctive species of finch. Darwin argued that the islands had originally been colonized by just one species of finch, but then in isolation, each island population had evolved in response to different environmental conditions. www.ingala.gov.ec/galapagosislands/images/stories/ingala_images/galapagos_take_a_tour/small_pics/galapagos_map_2.jpg

COEVOLUTION: Interaction Biodiversity Species so tightly connected, that the evolutionary history of one affects the other and vice versa.