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Mechanisms of Evolution Genetic ________ of individuals within a population makes evolution possible. ______ reproduction creates a large amount of this _________ as individuals inherit a combination of _______ (traits). In addition, __________ (permanent changes in DNA) happen randomly providing for the potential of new traits to _________ on their own. Although variation in a population occurs randomly, natural selection acts upon that variation in a non-random way. Evolution can be divided into two main categories: Macro-evolution is evolution on a ________, such as the evolution of a ___________ from a common ancestor Micro-evolution is the change in the __________________ (a shift in the ___________) within a population over time - it is evolution ____________________ Factors that can lead to the shift in gene frequencies include: Mutations - _________ changes in _____ that can affect the gene pool Gene Flow – The ________ of alleles from one population to another due to ___________. The addition of new alleles to a population will __________ diversity and may help the population survive. Non-random Mating - Individuals in a population select mates often based on their ___________ features. Examples: caribou antlers and peacock feathers Genetic Drift - Founder Effect - Change in gene frequencies because of ______________ events. Drift has a greater effect on ________ populations. a change in a gene pool that occurs when a few individuals _______ a new ___________ population. Example: island colonization. Bottleneck effect - a change in the gene pool caused by a ______________ in population. Example: natural disaster. Natural Selection - alleles that help an individual survive and reproduce will accumulate in the population, leading to a shift in the gene frequencies. Types of Selection Selective Pressures can result in different patterns of natural selection. Characteristics can be selected for (__________ selection) or against (_________ selection). Directional Selection – occurs when selection favours individuals with a more ___________ variation of a trait. The result is a shift away from the average condition. Example: strawberries are selected for larger and sweeter fruits, thoroughbred horses for running speed. Stabilizing Selection – occurs when the __________ characteristic within a population is favoured by the environment. Example: human birth weights are subject to stabilizing selection. Disruptive Selection – favours individuals at _________________________ of a characteristic. Example: male coho salmon – small 500 g or large 4500 g. Sexual Selection – the favouring of any trait that specifically enhances the _____________ of an individual. Sexual selection often leads to the males and females of a species evolving appearances and behaviours that are quite _______ from each other (________________). Example: males often evolved larger body size and other attributes (antlers) that are used in direct ___________ for mates. Some of the features selected for by sexual selection, can become a ___________ for the __________ of the individual. Example: large or brilliant coloured plumage make for easy prey. Patterns of Evolution Adaptive Radiation – occurs when a single species evolves into a number of distinct but _________ __________ species (Galapagos finches), usually occurs when a variety of new resources not being used by other species becomes available. Divergent Evolution - one or more new species are produced by changes to the initial organism ("___________"), each branch gives rise to a new species and "parent" can still exist. Example: Northern Ontario rodents – beaver, flying squirrel, porcupine Convergent Evolution – occurs when two different species evolve to occupy similar ecological _________. Example: streamlined body shape of the dolphin and shark Coevolution – a process in one species evolves in ___________ to the evolution of another species. Example: the Madagascar long-spurred orchid and the hawk moth