Reading Essentials for Biology Glencoe (794133), страница 41
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Read the terms and their definitions in the Mini Glossary above. Then, choose a term thatdescribes a type of structural adaptation. On the lines below, write a sentence using the term.____________________________________________________________________________________2. Use the table below to review what you have learned about adaptation. Write two types ofadaptations you read about in the first column. Write a fact about the rate at which the adaptation occurs in the second column, and an example of each type of adaptation in the third.Adaptation TableType of AdaptationRate at Which it OccursExampleVisit the Glencoe Science Web site at science.glencoe.com to find your biology book and learn more about natural selection and the evidence for evolution.168Chapter 15READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.____________________________________________________________________________________NameDateClassSection15.2 Mechanisms of Evolution◗ Before You ReadSC.F.2.4.3 The student understands the mechanisms of change (e.g., mutation and naturalselection) that lead to adaptations in a species and their ability to survive naturally inchanging conditions and to increase species diversity.
Also covers SC.D.1.4.1, SC.F.1.4.2,SC.G.2.4.3In this section you will learn about different ways that evolution occurs. For example, evolution canoccur when a physical barrier divides a population into smaller groups that can no longer interact.What barriers might divide a population? Write examples on the lines below.______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Population Genetics and EvolutionIn the previous section you learned about Darwin’s theory ofevolution by natural selection.
Since Darwin’s time, scientists havelearned about genes and have modified Darwin’s theories. Today,scientists look at the way genes act in plant and animal populations. This study is called population genetics. It is based on thethought that evolution happens when the genes in a populationchange over a long period of time.Individuals in a population do not evolve—populations do.Individuals’ genes do not change during their lifetime. But withina population, genes and their frequencies change over time.
Thisis what causes evolution.Identify MainIdeas Highlight the mainidea of each paragraph.What is genetic equilibrium?How can a population’s genes change over time? Picture all thealleles (the alternate forms of a gene) of a population’s genes in alarge group called a gene pool. The percentage of times anyallele is in the gene pool is called allelic frequency.
When thisfrequency stays the same over generations, genetic equilibriumexists. A population in genetic equilibrium is not evolving. Once achange happens, though, the population’s genetic equilibrium isdisrupted and evolution takes place.What can change genetic equilibrium?One way genetic equilibrium is disturbed is by mutation. Amutation is any change or random error in a DNA sequence.Some mutations simply occur by chance.
Radiation and chemicalscan also cause mutation.READING ESSENTIALS1. Analyze Which of thefollowing is an exampleof genetic equilibrium?(Circle your choice.)a. Generation after generation of a population of roses are red.b. A mutation in a population of red rosesresults in some yellowoffspring.Chapter 15169NameDateClassSection15.2Mechanisms of Evolution, continued2.
Analyze On what population would genetic driftmost likely have thegreatest impact? (Circleyour choice.)a. a population of twelveturtles on a small, isolated islandb. the population ofhumans in the UnitedStatesc. a population of 5000woodpeckers in western CanadaGenetic drift is another way that a population’s genetic equilibrium can be disrupted. Genetic drift is the change of allelicfrequencies by chance events. This change can greatly affectsmall populations made up of descendants of a small numberof organisms.For example, in Pennsylvania, there is a small Amish populationof about 12 000 people. The Amish marry only other members oftheir community.
Of the original 30 settlers in this community, atleast one carried a recessive allele that resulted in offspring withshort arms and legs and extra fingers and toes. Today, the frequency of this allele in this population is high—1 in 14. But, in therest of the United States, the frequency is lower, only 1 in 1000.Gene flow also can upset genetic equilibrium. Gene flowoccurs when an individual leaves or enters a population. Thisindividual’s genes either leave or enter the gene pool as a result.Mutation, genetic drift, and gene flow primarily affect smalland isolated gene pools. The impact is much smaller in larger, lessisolated gene pools.How do changes in a gene pool bring about evolution of anew species? Remember that a species is a group of living thingsthat look alike and can mate with each other to produce fertileoffspring.
The evolution of a new species is called speciation(spee shee AY shun). Speciation occurs when members of similarpopulations no longer mate with each other to produce fertile offspring. A new species could develop when part of a populationhas been geographically cut off from the rest of its population.The figure on page 171 illustrates this idea.An example would be when a river forms a physical barrier anddivides a population in two.
This is called geographic isolation.The separated parts of the population can no longer mate. Overtime, the gene pools of the now separate populations become verydifferent. In this way, natural selection results in new species.3. What is one way thatreproductive isolationcan occur?________________________________________________________________________170Chapter 15What happens in reproductive isolation?As populations become increasingly different from each other,reproductive isolation occurs.
This happens when organismsthat at one time mated with each other and produced fertile offspring are no longer able to do so. This can be because the geneticmaterial of the populations becomes so different that fertilizationcannot occur. Reproductive isolation also occurs if the matingseasons of similar populations are at different times of year.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.The Evolution of the SpeciesNameDateClassSection15.2Mechanisms of Evolution, continuedA Tree frogs are aCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.single population.BThe formation of a river maydivide the frogs into twopopulations. A new form mayappear in one population.C Over time, the dividedpopulations may become twospecies that may no longerinterbreed, even if reunited.What role do chromosomes play in thedevelopment of a new species?Chromosomes can also be important in the development ofnew species.
Many new types of plants and some types of animalsevolve as a result of what is called polyploidy (PAH lih ploy dee).Any individual or species with a multiple (an extra set) of the normal set of chromosomes is known as a polyploid. Mistakes duringmitosis or meiosis result in polyploid individuals. Some polyploidscannot produce offspring capable of reproducing.
But still othersdevelop into adults that can interbreed and a new species results.Many flowering plants and some important crops—such as wheat,cotton, and apples—originated by polyploidy.How much time does it take to develop anew species?Although the developing of new species by polyploidy takesonly one generation, most other types of speciation take muchREADING ESSENTIALSChapter 15171NameDateClassSection15.2Mechanisms of Evolution, continuedlonger. Gradualism is the idea that species originate through agradual change of adaptations. For example, fossil evidence showsthat sea lilies evolved slowly and steadily over time.Punctuated equilibrium is a theory that speciation occursquickly, in rapid bursts. There are long periods of genetic equilibrium between the bursts.
In this theory, environmental changeslike higher temperatures or a competitive species moving into apopulation’s habitat lead to fast changes in the population’s genepool. Fossil evidence shows several elephant species may haveevolved by punctuated equilibrium.Patterns of EvolutionExtinctmamoAmakihiPossibleancestralLasan finchCrestedhoneycreeperKauaiNiihauMolokaiOahuMauiLanaiAkialoaKahoolaweAkepaAkiapolaau172Chapter 15ApapaneMauiparrotbillLiwiAkikikiHawaiiGrosbeakfinchPalilaOuREADING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Biologists have observed that different patterns of evolutionoccur in different environments.
These patterns support the ideathat natural selection is important for evolution. An example ofthis occurs in the Hawaiian honeycreepers.Hawaiian honeycreepers are all similar in body size and shape,but they differ in color and beak shape. They also live in differenthabitats. Despite their differences, scientists hypothesize thatthese birds evolved from a single species that lived on theNameDateClassSection15.2Mechanisms of Evolution, continuedHawaiian Islands long ago. When a single ancestral speciesevolves into many different species that fit a number of differenthabitats, the result is called adaptive radiation.
Adaptive radiationis a type of divergent evolution. Divergent evolution occurs aspopulations that were once similar to an ancestral species changeand adapt to different living conditions. These populations eventually become new species.Another pattern that can occur is convergent evolution.Convergent evolution occurs when unrelated species live in similar environments in different parts of the world. Because theyhave similar environmental pressures, they share similar pressuresof natural selection. As a result, they have similarities. For example, there is an organ pipe cactus that grows in the deserts ofNorth and South America and a plant that looks similar and livesin African deserts.
These plants are not related, but their environments are similar. Both plants have fleshy bodies and no leaves.Convergent evolution has apparently occurred.4. What features dounrelated species thatdevelop similar traits indifferent parts of theworld demonstrate?________________________________________________________________________◗ After You ReadCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Mini Glossaryadaptive radiation: divergent evolution in whichancestral species evolve into a variety ofspecies that fit diverse habitatsallelic frequency: percentage of any specificallele found in a population’s gene poolconvergent evolution: evolution in which unrelated organisms evolve similar traits; occurswhen unrelated species occupy similarenvironmentsdivergent evolution: evolution in which speciesthat once were similar to an ancestralspecies diverge; occurs when populationschange as they adapt to different environmental conditions, eventually resulting innew speciesgene pool: all of the alleles available in apopulationgenetic drift: alteration of allelic frequencies in apopulation by chance events; disrupts apopulation’s genetic equilibriumgenetic equilibrium: condition in which the frequency of alleles in a population remains thesame over generations; no evolution occursREADING ESSENTIALSgeographic isolation: occurs whenever a physicalbarrier such as a river divides a population;results in individuals of the population nolonger being able to mate; can lead to theformation of new speciesgradualism: idea that species originate througha gradual change of adaptationspolyploid: any species with multiple sets of thenormal set of chromosomes; results fromerrors during mitosis or meiosispunctuated equilibrium: idea that periods ofspeciation occur relatively quickly with longperiods of genetic equilibrium betweenreproductive isolation: occurs when formerlyinterbreeding organisms can no longer produce fertile offspring due to an incompatibility of their genetic material or bydifferences in mating behaviorspeciation (spee shee AY shun): process of evolution of new species that occurs whenmembers of similar populations no longerinterbreed to produce fertile offspringwithin their natural environmentChapter 15173NameDateClassSection15.2Mechanisms of Evolution, continued1.
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