Genes and Variation Chapter 17 Study Guide

phenotype gene pool genotype alleles allele frequency 25 50 48% Heterozygo us 36% Homozygo us 16% Homzy gous 20 alleles for black fur and that is 40% 30 alleles for brown fur and that is 60% When scientists try to determine whether a population is evolving, they study it The allele frequency of an allele has nothing to do with whether the allele is dominant or recessive. In this mouse population, the recessive allele occurs more frequently than the dominant allele. A mutation is any change in the genetic material of a cell. Some mutations involve changes within individual genes. Other mutations involve changes in larger pieces of chromosomes. Some mutations— called neutral mutations—do not change an organism’ s phenotypeNote Sexual reproduction affects a populations genetic variation because the number of genotypes in each generation increases.Genes can be recommend during meiosis by crossing over and genetic recombination. Crossing-over is another way in which genes are recombined. Recall that crossing-over occurs during meiosis. In this process, paired. Lateral gene transfer is the passing of genes from one organism to another organism that is not its offspring. It increases variation when a species picks up new genes from different species. Polygenic Traits True Polygenic Single-gene trait alleles True True Refers to a characteristic or a phenotype that is controlled by one gene. Controlled by genes Bell-curved graph Each gene has two or more phenotypes Has many genotypes Genetic variation is the raw material of evolution, which can lead to different members of a population having different levels of fitness in a certain environment. The variation allows species to adapt to changes in their environment. Without such variation, the population would not evolve. The allele will die off. The allele will equal out. Single-gene trait, Natural selection on a single-gene trait can lead to changes in allele frequencies and The lighter fur color allele is decreasing in frequency and the darker fur color allele is increasing in frequency. Darker mice may be harder for predators to see, so they are more likely to survive and reproduce. Suppose a mutation causes a white fur phenotype to emerge in the population. If individuals with the new phenotype are more fit than the gray or black mice, the white allele may increase in frequency in the population. Black mice will likely continue to be more common than the other phenotypes Stabilizing selection would generally reduce the variation in a population. B C A allele frequency bottleneck effect founder effect founder effect Change in allele frequency Allele frequencieschange a The Hardy-Weinberg principlestates that allele frequencies in a population sh If a population is not evolving, allele frequencies in its gene pool do not chang Hardy-Weinberg principle predicts that fi ve conditions can disturb genetic equilibrium and cause evolution to occur: (1) nonrandom ti (2) ll l ti i d (3) i i ti i ti (4) When sexual selection is at work, genes for the traits selected for or against are not in equilibrium. ... They must mate with other species; the gene pools ft l ti tb t d d ti l i l t d The green insects will now blend in tho the habitat and the brown will become the hunted color because they cannot blend in. The formation of a new species iscalled speciation. They do not interbred and they produce fertile offspring. Populations must be reproductively isolated from one another. It can be behavioral, geographic, or temporal. When populations have differences in rituals or behaviors. When populations are separated by rivers, mountains, r bodies of water. Each of three similar species of orchid in the same forest release pollen on different days. The birds on the island may become reproductively isolated from the mainland birds through geographic isolation. As a result, the gene pool of the birds that colonized the island would remain isolated, and the birds may evolve to become a new species as they adapt to their island habitat finch polygenic South America Geographically Behaviorally Many years ago, a few finches from South America arrived on a Galápagos island. These finches were geographically isolated from the original South American population. They survived and reproduced. Over time, some finches from the first island may have migrated to a new island, becoming a new geographically-isolated population. Differing conditions on the two islands, such as varied food sources, may have caused the populations to evolve in separate ways. So, the allele frequencies in each population's gene pool would have also changed in different ways. Over time, migration, geographic isolation, and natural selection may have occurred multiple times on different Galápagos islands. Additionally, populations on different islands may have evolved separate breeding behaviors causing them to become behaviorally isolated. Competition among individuals and responses to a changing environment Reproductive isolation must occur so that the gene pools are isolated. When the gene pools are isolated, changes that occur in one gene pool will not be carried over to the other gene pool. Thus, over time, accumulated gene pool changes can produce a new species. Molecular clocks are pieces of DNA that mutate at a known rate. Scientists use molecular clocks to estimate how much time has passed since two species shared a common ancestor Neutral mutations accumulate in the DNA of different species at about hrs same rate because they are unaffected by natural selection here are many molecular clocks in a genome because some genes accumulate mutations faster than others. These different clocks allow researchers to time different kinds of events Species C; Species B and Species C have two mutations in common. Species B and Species A have no mutations in common. This shows that Species B and C are more closely related than Species B and A Species C and the species with Gene 2 do not share any mutations. D A Duplication in ancestor Mutation in one copy Original gene keeps original fu A change in Hox gene activity during embryonic development can change an organ-ism’ s body plan. Homologous Hox genes establish body plans in species that have not shared a common ancestor in hundreds of millions of years. In addition, major evolutionary changes may be based on Hox genes. A change in one Hox gene can result in major body changes in an animal. Scientists may be able to trace Hox gene changes to determine when and why certain species of organisms developed. genetic drift behavioral founder effect temporal single-gene trait bottleneck effect allele frequency gene pool True True geographic True speciation genetic equalibr stabilizing True