Origins of Life on Earth 4.7-4.8 Billion Year History

1. Origins of Life on Earth4.7-4.8 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)

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

3. 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. 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

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

5. 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

6. 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!

7. 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!

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

9. 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)

10. 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

11. 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

12. Transitions are more common than transversions because DNA repair enzymes can recognize wrong insertion representing a a transition better than a transversion

14. Variation • Some mutations will persist and increase genetic variationwithin a population. • Variants of a particular gene are known as alleles. • For example, the one of the genes for hair colourcomprises brown/blonde • alleles.

15. Natural Selection en.wikipedia.org/wiki/Image:Mutation_and_selection_diagram.svg • 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

16. 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.

17. 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

18. 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

19. 4 major mechanisms that drive evolution: • Natural Selection • Mutation • Gene Flow • Genetic Drift

20. 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

21. 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)

22. 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)

23. 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.   • 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

24. 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. Dogs are wolves www.puppy-training-solutions.com/image-files/dog-breed-information.jpg

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

26. 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.

27. 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 www.ingala.gov.ec/galapagosislands/images/stories/ingala_images/galapagos_take_a_tour/small_pics/galapagos_map_2.jpg

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