Chapter 18 Objectives and Vocabulary

Chapter 18 Objectives 1.​ Describe Evolution in genetic terms. Evolution in genetic terms is basically genes that produce phenotypes to increase their survival and their offspring in a particular environment will pass the genes for those traits on to their offspring. 2.​ Identify the sources of genetic variation. It is produced either by mutations, genetic recombination during sexual reproduction, or lateral gene transfer. 3.​ Explain what determines the phenotypes for a given trait. The phenotypes for a given trait is determined by how many genes control the specific trait. 4.​ Explain how natural selection affects single-gene and polygenic traits. Natural selection on single-gene traits affect simple changes in phenotype frequencies. On polygenic traits, natural selection affects the relative fitness of phenotypes in directional, stabilizing, or disruptive selection. 5.​ Define genetic drift. Genetic drift is when there is a random change in allele frequencies. 6.​ Describe the conditions required to maintain genetic equilibrium. To maintain genetic equilibrium there must be: nonrandom mating, small population sizes, gene flow from immigration or emigration, no mutations, and no natural selection. 7.​ Describe the types of isolation that lead to the formation of new species. Behavioral, geographic, and temporal isolation all lead to the formation of a new species. 8.​ Explain a current hypothesis about the speciation of the Galapagos finches. Speciation in Galápagos finches occurred by founding a new population, geographic isolation, changes in the new population’s gene pool, behavioral isolation, and ecological competition. 9.​ Identify where new genes come from New genes can come from either duplication or modification of already existing genes. 10.​Describe how Hox genes might be involved in evolutionary change. There would be a small amount of Hox genes involved that could result in big changes. 11.​Explain how molecular clocks work. Molecular clocks work on a relatively constant rate at which mutations occur. Mutations that are not subject to selection are used as “ticks” of the clock. Vocabulary- Write the definitions in your notebooks 1.​ Gene pool - all the genes, including different alleles for each gene, that are present in a population at any one time. 2.​ Allele frequency - the number of times that an allele occurs in a gene pool compared to the number of alleles in that gene pool for the same gene. 3.​ Single-gene trait - trait controlled by one gene that may have one or more alleles. 4.​ Polygenic trait - trait controlled by two or more genes, each with one or more alleles. 5.​ Directional selection - form of natural selection when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve 6.​ Stabilizing selection - form of natural selection in which individuals near the center of a distribution curve have higher fitness than individuals at either end of the curve 7.​ Disruptive selection - natural selection in which individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle of the curve 8.​ Genetic drift - random change in allele frequency caused by the series of chance occurrences that cause an allele to become more or less common in a population 9.​ Bottleneck effect - a change in allele frequency following dramatic reduction in the size of a population 10.​Founder effect - a change in allele frequencies as result of the migration of small subgroup of a population 11.​Genetic equilibrium - situation in which allele frequencies in a population remain the same from one generation to the next 12.​Hardy-Weinburg principle - principle that states that allele frequencies in a population remain constant unless one or more factors cause those frequencies to change 13.​Gene flow - movement of genes into or out of a population 14.​Speciation - formation of a new species 15.​Reproductive isolation - separation of a species or population so that they no longer interbred 16.​Behavioral isolation - form of reproductive isolation in which two populations develop differences in courtship rituals or other behaviors that prevent them from breeding 17.​Geographical isolation - form of reproductive isolation in which two populations are separated by geographic barriers such as rivers, mountains, or bodies of water, leading to the formation of two separate subspecies 18.​Temporal isolation - form of reproductive isolation in which two or more species reproduce at different times 19.​Hox gene - regulatory genes that determine which parts of an embryo develop into arms, legs, or wing