Evolution & Population Dynamics

Evolution & Population Dynamics Evolution & Natural Selection: Evolution induces small changes to POPULATIONS not INDIVIDUALS over TIME Natural Selection is the ability of some organisms to be better suited to survive to sexual maturity in order to pass on their genes (can even be used in order to select against bad traits such as short legged people running away from predators) This ONLY APPLIES TO GENETICS (heritable traits) and do not apply to things taught from parents to offspring Fitness & Fecundity: Fitness refers to an organism’s total ability to pass on traits to its offspring Fecundity refers to how easily and how often an organism can produce offspring and high fecundity is selected for (males will look for physically attractive women who therefore have higher fecundity) Alternative Selection: Group selection is the idea that genetic traits that benefit the population/group will still be selected for even if they don’t directly increase the fitness of the individual with the trait (such as “altruism” or “martyr”) and can apply to traits that are present even AFTER the reproductive age (such as a grandparent helping to take care of their grandchildren, giving them a better chance of surviving) Artificial selection (selective breeding) is when there is literally someone or something CHOOSING what traits they would like to see in the next generation (such as a farmer choosing to plant seeds from a larger tomato than from the smaller tomato for the next harvest) Stabilizing selection describes a process in which extremes of a trait (being very tall or very short for example) are selected against and an intermediary trait (like being average height) is selected for Genetic Drift, Bottleneck Effect, & Founder Effect: Genetic drift refers to random changes in populations that don’t increase or decrease overall fitness (for example with fur color of bunnies that don’t affect their chances of surviving) and works best with small populations Even favorable drifts can occur over time due to random chance 2 Types of Genetic Drift that cause extreme reduction in populations and are known as the Bottleneck Effect (some major disaster/event that kills off a lot of the population so only a little bit of the population is able to survive and therefore reproduce → don’t have to be favorable, just by random chance and often leads to lower levels of genetic diversity) and the Founder Effect (a smaller population that leaves the large one and forms a new “colony” and can lead to a lower level of diversity) Gene flow refers to alterations in the composition of a gene pool due to migration of individuals between different populations Assortative mating refers to a mating pattern and form of sexual selection in which individuals with similar phenotypes mate with one another more frequently than would be expected under a random mating pattern Directional selection occurs when one extreme of a trait is favored over another and the population starts to express that extreme phenotype more often Disruptive selection is a type of natural selection where that selects against the average individual in the population (two extreme phenotypes arise) Stabilizing selection occurs when natural selection favors the intermediate states of continuous variation (opposite of disruptive selection) Inbreeding: Inbreeding occurs when people in a population will selectively have offspring with a certain smaller group within that larger population (such as religion, culture, etc.) When inbreeding occurs in other species, it is almost always due to geographical barriers and the general population simply isn’t accessible Inbreeding can cause problems because individuals like you may also have recessive alleles that cause disease, and therefore would be more likely that you pass it on (autosomal recessive) while if you choose at random from a population, this is much less likely Autosomal dominant disorders are typically made aware in individuals who have them and they know the risks of having children, however autosomal recessive disorders are typically not known in the individuals who carry them Reproductive Isolation: Species that reproduce asexually have low genetic diversity while those that reproduce sexually have higher genetic diversity Reproductive isolation is the idea that there are many forces that stop two different organisms from having offspring together and have two categories: 1. Prezygotic Isolation: refers to all the different forces that prevent two organisms from having offspring with one another that occur prior to the formation of a zygote a. Temporal Isolation: refers to the fact that not all organisms mate at the same time (some at night/day, others in the spring/winter) b. Habitat Isolation: refers to the fact that not all organisms mate in the same place (some do in the forest and others in the desert) c. Behavioral Isolation: refers to mate selection and how organisms go about finding a mate (not all organisms attract mates the same way, i.e. birds sings and peacocks show their feathers) d. Mechanical Isolation: deals with the physical inability for two organisms to mate, even if they wanted to (such as an elephant mating with a mouse) e. Gametic Isolation: occurs when fertilization between the two gametes to form a zygote is impossible 2. Postzygotic Forms: refers to all the different forces that prevent two organisms from having offspring with one another that occur after the formation of a zygote a. Zygote Mortality: occurs when even if the two gametes from the two organisms fuse successfully to form a zygote, the zygote itself has a high mortality rate and is therefore unable to grow into a fully functional organism b. Hybrid Inviability: occurs when a zygote is able to grow into a mature organism but has a very high mortality rate and won’t be able to develop into a fully mature adult c. Hybrid Sterility: when the offspring is able to grow into a mature adult but is unable to mate and have offspring of its own If two organisms are not stopped by any of these barriers, then they are likely of the same species Evolution: Natural Selection & Human Selection Article: Three types of dog breeds: 1. Purebreds: type of dog that comes from a lineage of the same dog breed and has never mated with another breed 2. Cross breeds: type of dog that was the offspring of two purebreds 3. Mixed breeds: combination of multiple breeds where their parents weren’t purebreds Convergent Evolution refers to separate populations developing similar traits independently of one another (like Europeans and Africans developing a lactose tolerance without ever interacting with one another) Extra Notes: Analogous structures are structures that serve similar functions/purposes but come from different evolutionary origins Parallel evolution occurs when two related populations evolve similarly for a long period of time as they experience similar environmental conditions Adaptive radiation occurs when one lineage diverges into many others as isolated populations occupy different niches