AP Biology - Evolution
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The changes in a single gene pool.
The appearance of a major evolutionary development or a rare new species.
Occurs when one species replaces another.
Occurs when a new species branches out from a parent species.
Evidence for Evolution (6 areas)
- Fossil Record
- Comparitive Anatomy
- Comparative Biochemistry
- Comparative Embryology
- Molecular Biology
- By studying the fossil record, paleontology reveals the existence of species that have become extinct or have evolved into other species.
- Uses radioactive decay and half-life.
- Discovered Prokaryotes were the first organisms to develop on earth.
- Study of different structures contributes to scientists' understanding of anatomical structures and of evolutionary relationships.
- Homologous structures
- Analogous structues
- Vestigial structures
- Structures in different species that are similar in structure, because they have a common origin, but have different functions.
- Ex - The wing of a bat, the lateral fin of a whale, the hand of a human.
- Structures that have the same function but do not share a similar structure or have a common origin.
- Ex - The wing of a bug, the wing of a bird, the wing of a bat.
- Structures of no importance that were once important to ancestors.
- Ex - The human appendix, The whale pelvic bone.
- Organisms that have a common ancestor have common biochemical pathways. The more closely related the organisms are to each other, the more similar their biochemistry is.
- Ex - Humans and mice are both mammals. This close relationship allows researchers to test medicines on mice and conect results to humans.
- Closely related organisms go through simliar stages in their embryonic development.
- Comparison of the amino acid sequence of cytochrome c among different organisms shows which organisms are most closely related.
- Ex - The cytochrome c in human cells is almost identical to that of the chimpanzee and gorilla.
An iron-containing pigment present in the electron transport chain of all aerobes.
- Study of continental drift and fossils in different locations.
- See parallel evolution.
Believed that all life-forms can be arranged on a ladder of increasing complexity, each with its own alloted rung.
Carolus Linnaeus (Carl von Linne)
- Specialized in taxonomy.
- Believed that the classification system would reveal a divine plan.
- Developed the naming system: Binomial nomenclature
Branch of biology concerned with naming and classifying the diverse forms of life.
- System in which every organism has a unique name consiting of two parts:
- Genus name
- Species name
- Ex - The scientific name of humans is homo sapiens.
- Discovered that each stratum of earth is characterized by different fossils.
- Believed that a series of catastrophes was responsible for the changes in the organisms on earth and was a strong opponent of evolution.
Developed the theory of gradualism.
Developed theory of evolution bassed on the inheritance of acquired characteristics and use and disuse.
Inheritance of Acquired Characteristics
- Offspring gained triats that their parents 'acquired'.
- Ex - Giraffes stretch thier necks to reach food; their offspring then have long necks.
Use and Disuse
Traits are gained and lost based on use of that trait.
- Visited the Galapagos Islands among other places.
- Developed his theory of natural selection.
Darwin's Theory of Natural Selection
- Populations tend to grow exponentially, overpopulate, and exceed their resources.
- Overpopulation results in competition and a struggle for existence.
- There is variation and an unequal ability of individuals to survive and reproduce.
- Only the best-fit individuals survive and get to pass on their traits to offspring.
- Evolution occurs as advantageous traits accumulate in a population.
- Eliminates the extremes and favors the more common inextremediate forms.
- Ex - In humans, stabilizing selection keeps the majority of birth weights in the 6-8 pound range. For babies much smaller and larger, infant mortality is greater.
- Increases the extreme types in a population at the expense of intermediate forms.
- May result in balanced polymorphism.
- Ex - An enviornment that has very light rocks and very dark soil. There are light, intermediate-colored, and dark mice. The intermediate-colored mice would die out because of preditation.
- In which one phenotype replaces another in the gene pool as a result of changing enviornment conditions.
- Ex - Light peppered moths survived well in England while dark peppered moths were hunted. After polution there were more dark peppered moths and less light peppered moths, because the light trees became dark.
- Ex - Antibiotics killed susceptible bacteria; Those that were resistant to the antibiotics replaced them in the next generation.
- Selection based on variation in secondary sexual characteristics related to competing for and attracting mates.
- Ex - Lionesses instinctively choose lions with long dark manes because it indicates high levels of testosterone, which leads to better offspring.
Humans breed plants and animals by seeking individuals with desired traits as breeding stock.
Sources of Variation in a Population
- Balanced polymorphism
- Geographic variation
- Sexual reproduction
- Heterozygote superiority
- Frequency-dependent selection
- Evolutionary neutral traits
- The presence of two or more phenotypically distinct forms of a trait in a single population of a species.
- Ex - black and white peppered moths.
- Variation in geographic regions lead to different adaptations.
- Cline - graded variation in the phenotype of an organism because of type of enviornment.
- Provides variation due to the shuffling and recombination of alleles during meiosis and fertilization.
- Independent assortment of chromosomes, during metaphase I, results in the recombination of unliked genes.
- Crossing-over is the exchange of genetic material of homologous chromosomes and occurs during meiosis I.
- The random fertilization of one ovum by one sperm out of millions results in enormous variety among the offspring.
- The mating of organisms within one species that are not closely related.
- Maintains both variation within a species and a strong gene pool.
- Ex - The dominant male lion of a pride chases away the young maturing males before they become sexually mature. This prevents inbreeding with their female siblings.
The 2n condition, maintains and shelters a hidden pool of alleles thta may not be suitable for present conditions but that could be advantageous when contitions change.
- Preserves multiple alleles in a population. It is a phenomenon in which the hybrid individual is selected for because it has greater reproductive success.
- Ex - Siclkle cell anemia. Those with homozygous recesive have sickle cell anemia. Those with homozygous dominant are susceptible to and may die of malaria. Those that are heterozygous do not suffer from sickle celll anemia and are resistant malaria.
- This acts to decrease the frequency of the more common phenotypes and increase the frequency of the less common ones.
- Ex - predators develop a search image, or standard representation of prey, that enables them to hunt a particular kind of prey effectively. Less common individuals, that may look different are not prayed upon as frequently as the most common type.
Evolutionary Neutral Traits
- These are traits that seem to have no selective value, but perhaps actually influence survival and reproductive success in ways that are difficult to measure.
- Ex - Blood type and fingerprint variation.
Causes of Evolution of a Population
- Genetic drift
- Gene flow
- Nonrandom mating
- Natural selection
- The change in the gene pool due to chance.
- Bottleneck effect
- Founder effect
Natural disasters such as fire, earthquake, and flood reduce the size of a population unselectively, resulting in a loss of genetic variation. The resulting population is much smaller and not representative of the original one. Certain alleles may be under or overrepresented compared with the original population.
- When a small population breaks away from a larger one to colonize a new area, it is most likely not genetically representative of the original larger population. Rare alleles may be overrepresented.
- Ex - Germans came to the new world with a rare dominant gene 'polydactyly', which results in having extra fingers and toes. Their isolation and intermarriage of the close community lead to the population now having a high incidence of polydactyly.
- Movement of alleles into or out of a population.
- Ex - pollen from one valley can be carried by the wind across a mountain to another valley.
Changes in genetic material and are the raw material for evolutionary change.
- Individuals choose their mates for a specific reason. This selection of a pate serves to eliminate the less-fit individuals.
- Ex - Lionesses instinctively choosing mates with large dark manes.
Major mechanism of evolution in any population. Those individuals who are better adapted in a particular enviornment exhibit better reproductive success. The most successful traits for survival are passed down to offspring.
Hardy-Weinberg Equilibrium (Characteristics)
- The poplulation must be very large.
- The population must be isolated from the other population.
- There must be no mutations in the population.
- Mating must be random.
- No natural selection.
- A population whose members have the potential to interbreed in nature and produce viable, fertile offspring.
- Species is defined in terms of reproductive isolation, meaning that one group of genes becomes isolated from another to begin a separate evolutionary history.
The evolutionary process by which new species arise.
The formation of new species caused by a separation by geography, such as mountain ranges, canyons, rivers, lakes, glaciers, altitude, or longitude.
Isolation caused by physical features such as mountain ranges, canyons, rivers, lakes, or glaciers.
- The formation of new species without geographic isolation.
- Habitat/Ecological Isolation
- Behavioral Isolation
- Temporal Isolation
- Mechanical Isolation
- Gametic Isolation
- The condition where a cell has more than two complete sets of chromosomes.
- Ex - Plants that are polyploidy cannot breed with others of the same species that are not polyploidy.
- Two organisms live in the same area but encounter each other rarely.
- Ex - Two species of one genus snake can be found in the same geographic area, but one inhabits the water while the other is mainly terrestrial.
- Form of reproductive isolation in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding.
- Ex - Male fireflies of various species signal to females of their kind by blinging in a particular pattern. If the female does not respond with the correct blinking pattern, no matting occurs.
- Species that breed during different times of day, different seasons, or different years cannot mix gametes.
- Ex - Eastern and western spotted skunk overlap in range, but the eastern ones mate in late winter where as the western ones mate in late summer.
- Physical differences in reproductive organs can prevent successful mating.
- Ex - A small male dog cannot mate with a large female dog.
- Sperm of one species may not be able to fertilize eggs of another species.
- Biochemical barrier - sperm cannot penetrate egg.
- Chemical incompatibility - sperm cannot survive in female reproductive tract.
Occurs when a population becomes isolated (for any reason) from the rest of the species, becomes exposed to new selective pressures, and evolves into a new species.
- When unrelated species occupy the same enviornment, they are subjected to similar selective pressures and show similar adaptations.
- Ex - Sharks and dolphins
- When two related species that have made similar evolutionary adaptations after their divergence from a common ancestor.
- Ex - Marsupial animals of Australia vs placental mammals of North America - sugar glider (m) vs flying squirrel.
- The reciprocal evolutionary set of adaptations of two interacting species.
- Ex - Monarch butterfly and the mildweed plant. The milkweed plant contains poisons that deter herbivores from eating them. Monarch butterflies lay their eggs in the plant and the larvae will feed on the weed and absorb the poison. When they become adult butterflies they contain the poison which makes the bug toxic.
- The emergence of numerous species from a common ancestor introduced into a new enviornment.
- Ex - Darwin's finches that live on the Galapagos Islands today diverged from a single species. There are currently 6 ground finches, 6 tree finches, and 1 warbler finch.
Theory that organisms descend from a common ancestor gradually, over a long period of time, in a linear or branching fashion.
Theory proposes that new species appear suddenly after long periods of stasis. A new species changes most as it buds from a parent species and then changes little for the rest of its existence.
- The experiment that mimics life's early characteristics.
This theory states that mitochondria and chloroplasts were once free-living prokaryotes that took up residence inside larger prokaryotic cells in a permanent, symbiotic relationship.
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