Population and Evolution

I. Population and Evolution

1. The process by which modern organisms have descended from ancient organisms is called evolution. 2. Charles Darwin contributed more to our understanding of the process of evolution than anyone else. a. His research was done in various locations, but primarily in the Galapagos Islands. b. His research was on finches c. His research spanned over a 30 year period. d. He found that many different organisms existed. e. It is estimated that 3 million to more than 20 million different species live today. f. More than 99.9% of species that once lived are now extinct. 3. Fitness is the physical traits and behaviors that enable an organism to survive and reproduce in their environment. 4. Many theories prior to Darwin existed on how life came about and how organisms adapt to their environment. a. Lamarck: organisms change b/c they want to better themselves and become more fit for their env. i. Use and Disuse: Lamarck believed that change occurred b/c organisms could alter their shape by using their bodies in different ways or not using a body part. Ex. Giraffes neck ii. Acquired traits: acquired traits were inherited. Ex. Weight lifters and their muscle mass. 5. Darwin published the Origin of Species by Means of Natural Selection. a. Modern organisms have been produced through evolution b. It is a slow, long process of change in species over time. c. All species have shared, or common ancestors, this is called common descent. d. Adaptation -fitness arises through adaptation, which enable organisms to become better suited for their environment. e. Any inherited characteristic that increases an animal’s or plant’s fitness for survival. Ex. Giraffes neck II. Fossils 1. 18th and 19th century people theorized that the earth was older than people originally though. 2. James Hutton and Charles Lyell came up with evidence that this was indeed true. a. Rain, heat, cold and active volcanoes etc. change rocks, mountains and valleys; which happens slowly over a long period of time (longer then just thousands of years in some cases). b. Others found that life has changed over time by examining fossils. i. Fossils are preserved remains of ancient organisms. 3. Geologic Time Scale a. This is a record in the rocks b. Depending on the position of layers of rock relative to each other determines the age of the rock. c. Lower rock layers were deposited before the upper layers. i. Lower layers are older than upper layers provided they have not been disturbed in any way. ii. Relative dating-technique to determine the age of fossils relative to other fossils in different layers of rock.

d. Rocks are made of various elements, some are radioactive. i. Radioactive elements decay (break down) into nonradioactive elements at a very steady rate. ii. The measurement for decay is Half-Life. 1. length of time required for half the radioactive atoms in a sample to decay. *example in pictures: 1st picture original amount of isotope; next picture half the isotope left; 3rd picture half of 2nd pictures isotopes left

If the half life of an element is 1 million years… Time Amt of radioactive element (millions of yrs) (kg) 4 1 3 .5 2 .25 1 .125 present .0325

iii. each element has a different half life iv. They provide natural “clocks” v. Can help date rocks, and specimens of different ages; called absolute dating. vi. Earth is about 4.5 billion years old. e. The fossil record shows us that change followed change on Earth due to change in climate etc. i. It’s a preserved collective history of the Earth’s organisms. ii. Shows major changes in earths climate and geography 1. ex. Shark teeth in Arizona 2. Show’s that whales once lived on land 3. Fossils of dinosaurs

III. Theory of Natural Selection 1. works over long periods of time and without any goal or purpose and is governed by chance.

A. Survival of the Fittest 1. Individuals whose characteristics are well suited to their environment survive and reproduce, thus passing on their traits. 2. Individuals not well suited will die or leave fewer offspring. Ex. Peppered Moths 1. natural Selection in action 2. 19th century England, trunks of oak trees a light brown; there were two types of moths, light and dark. The light moths blended in, the dark moths stood out. 3. Industrial revolution began in England; lots of pollution; stained the trunks dark brown. 4. more and more moths with dark coloration were appearing, why? 5. Birds eating moths they could see; darker moths surviving and reproducing, therefore more dark moths appear.

Light Moth

Dark moth

IV Genetic Change and Variation 1. Genes are a source of random variation in a population. 2. Mutations cause some variation 3. Crossing over causes variation

A. Evolution as Genetic Change 1. Populations: collection of individuals of the same species in a given area whose members can breed with one another. a. Ex. All the fish of a certain species in a single pond= 1 population; individuals in a separate pond would be another population. 2. Because all members of a population can interbreed, they and their offspring share a common group of genes, called a gene pool. a. each contains a certain amount of alleles for each trait.

b. Number of times an allele occurs in a gene pool compared with the number of times other alleles for the same gene occur is relative frequency. i. Ex. Deck of cards: shuffling and reshuffling produce a lot of variety of different hands. Shuffling alone will not change the number of aces, kings, queens etc 3. Species: group of similar looking organisms that breed with one another and produce fertile offspring in a natural environment. a. They share a common gene pool b. Genetic change in one individual can spread through the population as they mate. c. If it increases fitness, that gene will be found in many individuals d. Many organisms can evolve together with their environment. 4. Biotic Potential: rate at which a population will grow if all individuals survive and reproduce at maximum capacity! a. In nature, most don’t reach their biotic potential b/c of shortage of food, space, predators or too much waste. b. Organisms reach a maximum then start to decline until there’s a balance between individuals and resources. c. Growth Curve: used to study patterns of population growth=# of individuals and resources. i. J shape curve=tracks 2 phases of growth a. exponential-increase rapidly b. lag phase-little or no growth occurs

Exponential growth

ii.. S shape Curve: period of stability, - gives carrying capacity-maximum # of individuals in a population - Predators, disease etc. keep population in check. - Ex. Rabbits in Australia; there was no disease or predators therefore the population of rabbits reproduced at a high rate and there was an overpopulation of rabbits.

(Exponential) (lag) V. Development of New species 1. New species form when populations are isolated or separated, this is known as reproductive isolation. a. Isolated so they don’t interbreed b. Occurs in many ways i. Geographic barriers ex. Rivers, mountains etc ii. Difference in courtship behavior or fertile periods 2. Adaptive Radiations or Divergent Evolution a. One species gives rise to many species as they adapt to new conditions b. Develop characteristics to survive in many niches (where the organism fits into the world; ex. Food it its, where it lives etc.) c. Cladogram: shows how different groups of living organisms are related to one another and to their ancestors.

d. Seen in homologous structures-structures similar between different organisms i. Ex. Dogs leg vs bats wing vs. humans arm vs. whales flipper 3. Convergent Evolution a. Produce species that are similar in appearance and behavior, even though they are not closely related. b. Produced many analogous structures i. Similar in appearance and function but have different origins. 1. wings of birds, bats and butterflies allow them to fly, but made differently (birds have skin, muscles and bones, butterflies wing is a membrane and bats have skin stretched between finger bones). VI. Genetic Drift 1. Don’t always need natural selection for evolution 2. an allele can become more or less common in a population by chance in a small population. a. One individual with a certain allele may produce more offspring than another individual (just by chance), thus, the allele is seen more in that population. Ex. Huntingtons disease in Island populations. Ex. The Amish and 6 finger dwarfs. b. environmental events can wipe out many individuals in a population. i.Occurs most efficiently in small populations b/c chance events, such as hurricanes and Tsunami’s, are less likely to affect all members of a very large population.

* ALL characteristics of an organism do not have to contribute to fitness. Ex. Indian rhino (1 horn) vs African rhino (2 horns) Ex. African camel (1 hump) vs asian camel (2 humps)

VII. Gradual and Rapid Evolutionary Change. 1. Gradualism: theory that evolutionary change is slow and steady 2. Equilibrium: when groups of animals and plants do not change very much. 3. Mass extinction: where many species vanish at once (due to changes on Earth, such as climate etc). example: dinosaur extinction 4. Punctuated equilibrium is long stable periods interrupted by brief periods of change. a. Steven Gould came up with this theory b. Very controversial c. However, seen that evolution proceeds at various rates. VIII. Hardy-Weinberg Principle-a control for measuring evolution. 1. States that allele frequencies in a population will remain constant unless one more more factors cause those frequencies to change. a. 5 conditions are required to maintain genetic equilibrium (allele frequencies remain constant) from generation to generation i. Random mating-ensures that each individual has an equal chance of passing on its alleles to offspring. ii. Large population-genetic drift has less effect on large populations. iii. No movement in or out of the population-to ensure no new alleles are brought into the population. iv. No mutations-mutations would change allele frequency in the population. v. No natural selection-all genotypes must have equal probabilities of survival and reproduction and no phenotype can have a selective advantage over another. 2. Two Equations: p2 + 2pq + q2 = 1 AND p + q =1 p = frequency of dominant allele (A) q = frequency of recessive allele (a) p2 = frequency of Homozygous Dominant genotype (AA) (% of Homozygous Dominant individuals) 2pq = frequency of heterozygous genotype (Aa) (% of Heterozygous individuals) q2 = frequency of Homozygous Recessive genotype (aa) (% of Homozygous Recessive individuals) Practice:  If 98 out of 200 individuals in a population express the recessive phenotype, what percentage of the population would you predict to be heterozygotes?  (a) I have given you information on the frequency of the homozygous recessive (or q2). So start by determining q2 and then solving for q.  q2 = (98/200) = 0.49 (or 49%)  q = square root of 0.49 = 0.7 (70%)  (b) Now that you have q, you can solve for p. Remember there are only two alleles in the population, so if you add the frequency of the two alleles, you have accounted for all possibilities and it must equal 1. So p + q = 1.  p = 1-q  p = 1 - 0.7 = 0.3 (30%)  (c) Now what is the formula for heterozygotes? Think back to the Hardy-Weinberg equation -- it is dealing with the genotypes of individuals in the population.  p2 + 2pq + q2 = 1  frequency of homozygous dominant + frequency of heterozygotes + frequency of homozygous recessive = 1  so.....2pq = frequency of heterozygotes  frequency of heterozygotes = 2 (0.3)(0.7) = 0.42 or 42%  (d) Now that you have figured out the % of heterozygotes, can you figure out the % of homozygous dominant? Does the % of homozygous dominant, heterozygotes and homozygous recessive individuals add up to 100%? If not, you have made an error. Those are the only three genotypes possible with only two alleles and a simple dominant and recessive relationship.  p2 = (0.3)(0.3) = 0.09 (or 9%)  p2 + 2pq + q2 = 1  0.09 + 0.42 + 0.49 = 1.0

Evidence of Evolution (recap): 1. Fossil Record 2. Homologous structures 3. Analogous structures 4. vestigial structures 5. Molecular biology 6. embryology