Lab5_evolution

Lab5_evolution - Evolution A population is a group of...

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1 Evolution •A population is a group of individuals from the same species that live and breed together. Theory of evolution states that species are related and change through time. Evolution —the genetically based change in a population's traits over time. • Evolution is often defined as change in a population's allele frequencies (genetic makeup) over time. • The four mechanisms that cause evolution are: (1) Natural selection; (2) Genetic drift; (3) Gene flow; and (4) Mutation 1. Natural Selection • Darwinian fitness - differential survival and reproduction influenced by the heritable traits • Natural selection occurs when individuals with certain heritable phenotypes survive and reproduce better than others. • The alleles responsible for the increased reproduction then increase in frequency. •An adaptation is a heritable trait that increases an individual's fitness in a particular environment relative to individuals lacking that trait. – Not all traits are adaptive .
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2 Natural Selection • Selection acts on individuals, but evolutionary change occurs in populations. – Individuals do not change during natural selection. – Those that are selected produce more surviving offspring than other individuals do, causing a change in the genetic makeup of the population. • Natural selection maintains genetic variation in a population. • Different patterns of natural selection exist, each with its own causes and consequences. 1.1 Directional selection 1.2 Stabilizing selection 1.3 Disruptive selection 1.4 Sexual selection 1.1 Directional Selection Directional selection occurs when natural selection increases the frequency of one allele. • Directional selection reduces population genetic diversity over time. • If directional selection continues long enough, the favored alleles are fixed (eventually reach a frequency of 100%) and the unfavored alleles are lost .
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1.2 Stabilizing Selection Stabilizing selection occurs when individuals with intermediate traits reproduce more than others, thereby maintaining intermediate phenotypes in a population. • Stabilizing selection decreases a population's genetic variation over time but does not change its average trait value. 1.3 Disruptive Selection Disruptive selection occurs when intermediate phenotypes are selected against and extreme phenotypes are favored. • Disruptive selection maintains genetic variation but does not change the mean value of a trait. • Disruptive selection can cause
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Lab5_evolution - Evolution A population is a group of...

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