Mechanisms of Evolution PDF

MECHANISMS OF EVOLUTION Mr. Marvin M.Feliciano, LPT CONCEPT: In biology, EVOLUTION is the change in the characteristics of a species over several generations and relies on the process of natural selection. The theory of evolution...

MECHANISMS OF EVOLUTION Mr. Marvin M.Feliciano, LPT CONCEPT: In biology, EVOLUTION is the change in the characteristics of a species over several generations and relies on the process of natural selection. The theory of evolution is based on the idea that all species are related and gradually change over time. CONCEPT: Evolution relies on there being genetic variation in a population which affects the physical characteristics of an organism. Some of these characteristics may give the individual an advantage over other individuals which they can then pass on to their progeny. MECHANISMS OF EVOLUTION 1. Natural Selection 2. Gene Flow 3. Mutations 4. Genetic Drift 5. Non-Random Mating  MECHANISMS OF EVOLUTION 1.Natural Selection  MECHANISMS OF EVOLUTION 1.Natural Selection - Affects variation in a population as the better adapted (more fit) individuals to their environment survive and reproduce, passing on their genes to the successive generations increasing the frequency of favorable alleles in the population. - As a consequence those individuals most suited to their environment survive and, given enough time, the species will gradually evolve.  MECHANISMS OF EVOLUTION 1.Natural Selection - Individuals with characteristics best suited to their environment are more likely to survive, finding food, avoiding predators and resisting disease. These individuals are more likely to reproduce and pass their genes on to their children. - Nature “selects” which organisms will be successful  MECHANISMS OF EVOLUTION  Types of Natural Selection 1. Directional Natural Selection - Occurs when individuals at one end on the frequency distribution are better adapted to the environment than those in the middle  MECHANISMS OF EVOLUTION  Types of Natural Selection 1. Directional Natural Selection - This type of natural selection occurs when selective pressures are working in favour of one extreme of a trait. Therefore when looking at a distribution of traits in a population, a graph tends to lean more to one side: Example: Giraffes with the longest necks are able to reach more leaves to each. Selective pressures will work in the advantage of the longer neck giraffes and therefore the distribution of the trait within the population will shift towards the longer neck trait.  MECHANISMS OF EVOLUTION  Types of Natural Selection 2. Disruptive Selection - Occurs when individuals near the upper and lower ends of the distribution are better adapted than those in the middle  MECHANISMS OF EVOLUTION  Types of Natural Selection 2. Disruptive Selection - This type of natural selection occurs when selective pressures are working in favour of the two extremes and against the intermediate trait. This type of selection is not as common. When looking at a trait distribution, there are two higher peaks on both ends with a minimum in the middle as such: Example: Short tails help keep predators from catching you on the ground. Long tails are good for balance in the trees. Medium tails don’t help.  MECHANISMS OF EVOLUTION  Types of Natural Selection 3. Stabilizing Selection - Occurs when individuals near the center of the distribution are more fit than individuals at either end  MECHANISMS OF EVOLUTION  Types of Natural Selection 3. Stabilizing Selection - This type of natural selection occurs when there are selective pressures working against two extremes of a trait and therefore the intermediate or “middle” trait is selected for. If we look at a distribution of traits in the population, it is noticeable that a standard distribution is followed: Example: For a plant, the plants that are very tall are exposed to more wind and are at risk of being blown over. The plants that are very short fail to get enough sunlight to prosper. Therefore, the plants that are a middle height between the two get both enough sunlight and protection from the wind MECHANISMS OF EVOLUTION 2. Gene Flow  MECHANISMS OF EVOLUTION 2. Gene Flow - aka “Gene Migration” - is the movement of populations or group of individuals or species, also drives evolution - happens when migrating individuals breed in their new location MECHANISMS OF EVOLUTION 2. Gene Flow - Concepts: a.When an individual leaves a population, it takes its genes with it b.When an individual enters a population, it introduces new genes Some individuals from a population of brown beetles might have joined a population of green beetles. That would make the genes for brown beetles more frequent in the green beetle population. MECHANISMS OF EVOLUTION 3. Mutation  MECHANISMS OF EVOLUTION 3. Mutation - is a change in DNA the hereditary material of life. An organism’s DNA affects how it looks, how it behaves, and its physiology — all aspects of its life. So a change in an organism’s DNA can cause changes in all aspects of its life. - is inheritable trait of genotype - provides the variation that can be acted upon by natural selection  MECHANISMS OF EVOLUTION 3. Mutation - Somatic mutation: occurs in non-reproductive cells and won’t be passed onto offspring MECHANISMS OF EVOLUTION 3. Mutation - Causes: a. DNA fails to copy accurately b. External influences can create mutations c. Exposure to specific chemicals or radiations  MECHANISMS OF EVOLUTION 1. Natural Selection 2. Gene Flow 3. Mutations 4. Genetic Drift 5. Non-Random Mating  MECHANISMS OF EVOLUTION 4. Genetic Drift  MECHANISMS OF EVOLUTION 4. Genetic Drift - random changes in gene pool (collection of genes in population) - Smaller population sizes are more susceptible to genetic drift than larger populations because there is a greater chance that a rare allele will be lost. - CONCEPTS: a. It happens to all population b. Has drastic effect in SMALL population c. Driven by chance, not selection  MECHANISMS OF EVOLUTION 4. Genetic Drift - TWO TYPES: a. Founder Effect – small group leaves with varying gene frequency  MECHANISMS OF EVOLUTION 4. Genetic Drift - TWO TYPES: a. Bottleneck Effect – random reduction in population that changes the gene pool Imagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation—but just by chance. These chance changes from generation to generation are known as genetic drift MECHANISMS OF EVOLUTION 5. NON-RANDOM Mating  MECHANISMS OF EVOLUTION 5. NON-RANDOM Mating - In animals, non-random mating can change allele frequencies as the choice of mates is often an important part of behavior  MECHANISMS OF EVOLUTION 5. NON-RANDOM Mating a. Hardy Weinberg Principle -This condition can be modeled as the Hardy-Weinberg Equilibrium (maintain genetic equilibrium), which requires: 1. Random Mating - all members of the population must have an equal opportunity to produce offspring  MECHANISMS OF EVOLUTION 5. NON-RANDOM Mating a. Hardy Weinberg Principle -This condition can be modeled as the Hardy- Weinberg Equilibrium (maintain genetic equilibrium), which requires: 2. Population size is large 3. No selection occurs 4. All genotypes can survive and reproduce equally 5. No mutations THANK YOU! 