12Artificial selection- Modifying species by selecting desired traits and breeding them.3Natural selection- A selection process that occurs in nature by environmental factors that allows only certain organisms to reproduce and survive. allows only certain organisms to reproduce and survive. 4Extinction- An irrevocable loss of a species.567Strata (layers)- The relative ages of fossils are determined by the layer on which they are found. The top layer of strata is the youngest.found. The top layer of strata is the youngest.A fossil record provides some of the strongest evidence of evolution because of the sequence in which fossils appear within layers of rocks.Radioactive dating is also used to determine a fossils age. 89Homologous structures- Features that have different functions but are structurally similar because of common ancestry.because of common ancestry.10Evolutionary trees show patterns of decent.11Gene pool- the total collection of genes in a population at any one time.Population-A group of individuals of the same species living in the same place at the same Population-A group of individuals of the same species living in the same place at the same time.12New alleles originate by MUTATION, which is a change in nucleotide sequence of DNA.Mutation and sexual reproduction give genetic variation, making evolution possibleMutation and sexual reproduction give genetic variation, making evolution possible1314Types of Genetic Drift:Bottleneck effect-A drastic reduction in population size and change in allele frequencies.Bottleneck effect-A drastic reduction in population size and change in allele frequencies.Founder effect- Difference in the gene pool of a small colony compared with the original population.Gene flow- where a population may gain or loose alleles when fertile individuals move into or out of a population or when gametes are transferred between populations.15Stabilizing direction- favors intermediate phenotypes Directional selection-Shifts the overall makeup of the population by acting against Directional selection-Shifts the overall makeup of the population by acting against individuals at one of the phenotypic extremes.Disruptive direction- Favors individuals at both extremes of a phenotypic range.1617Sexual Dimorphism- noticeable differences, not directly associated with reproduction or survival. survival. Sexual selection- A form of natural selection in which individuals with certain characteristics are more likely than other individuals to obtain mates. Intrasexual selection- When some species secondary sex structures may be used to compete with members of the same sex for a partner.Intersexual selection- Individuals of one sex are choosy in selecting their
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