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AP Biology Chapter 23 Notes The Evolution of Populations What you need to know… How ____________________ and ____________________ reproduction each produce genetic __________________. The conditions for ______________________________________ equilibrium. How to use the Hardy-Weinberg equation to calculate allelic ________________________ and to test whether a population is _______________________. _______________________________ - change in allele frequencies over generations Concept 23.1: Mutation and sexual reproduction produce the genetic variation that makes evolution possible Two processes produce the variation in gene pools that contributes to differences among individuals o ____________________________________ o ____________________________________ reproduction _________________________ characters can be classified on an either-or basis _________________________ characters vary along a continuum within a population ___________________________________________ measures the average percent of loci that are heterozygous in a population Most species exhibit _______________________________ variation, differences between gene pools of separate populations or population subgroups Some examples of geographic variation occur as a ____________________, which is a graded change in a trait along a geographic axis _______________________ are changes in the nucleotide sequence of DNA o Mutations cause ____________ genes and alleles to arise o Only mutations in cells that produce gametes can be ____________ to offspring o A ______________ mutation is a change in one base in a gene The effects of point mutations can vary: in _____________________ regions of DNA are often harmless in a _____________ might not affect protein production because of redundancy in the genetic code Mutations that result in a change in protein production are often _______________ Mutations that result in a change in protein production can sometimes _________________ the fitness between organism and environment o Mutation _______________ are low in animals and plants The average is about one mutation in every 100,000 genes per generation o Mutations __________________ are often lower in prokaryotes and higher in viruses Concept 23.2: The Hardy-Weinberg equation can be used to test whether a population is evolving A ___________________________ is a localized group of individuals capable of interbreeding and producing fertile offspring A _______________ pool consists of all the alleles for all loci in a population A _________________ is fixed if all individuals in a population are homozygous for the same allele The frequency of an allele in a population can be calculated o For diploid organisms, the total number of alleles at a locus is the total number of individuals x 2 o The total number of dominant alleles at a locus is 2 alleles for each homozygous dominant individual plus 1 allele for each heterozygous individual; the same logic applies for recessive alleles o If there are 2 alleles at a locus, p and q are used to represent their frequencies the frequency of all alleles in a population will add up to 1 For example______________________________________ The ___________________________________ principle describes a population that is not evolving o If a population does not meet the criteria of the Hardy-Weinberg principle, it can be concluded that the population is evolving The ______________________________________ principle states that frequencies of alleles and genotypes in a population remain constant from generation to generation o _______________________________________ o where _________ and _________represent the frequencies of the homozygous genotypes and ________ represents the frequency of the heterozygous genotype The five conditions for nonevolving populations are rarely met in nature: o No ________________ o ____________________ mating o No _____________________________________ o Extremely ________________ population size o No _______________ flow Concept 23.3: Natural selection, genetic drift, and gene flow can alter allele frequencies in a population Three major factors alter allele frequencies and bring about most evolutionary change: o ________________________________ o ________________________________ o ________________________________ Genetic ___________________ describes how allele frequencies fluctuate unpredictably from one generation to the next o Genetic drift tends to ____________________ genetic variation through losses of alleles o The _________________________ effect occurs when a few individuals become isolated from a larger population Allele frequencies in the small founder population can be ______________________ from those in the larger parent population o The __________________________ effect is a sudden reduction in population size due to a change in the environment The resulting gene pool may no longer be reflective of the original population’s gene pool If the population remains ________________, it may be further affected by genetic drift o Effects of Genetic Drift: A Summary Genetic drift is significant in ____________________ populations Genetic drift causes ______________________ frequencies to change at _________________ Genetic drift can lead to a ____________________ of genetic variation within populations Genetic drift can cause ________________________ alleles to become fixed Gene ________________ consists of the movement of alleles among populations o Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen) o Gene flow tends to _________________ differences between populations over time o Gene flow is more likely than mutation to _______________ allele frequencies directly o Gene flow can ____________________ the fitness of a population Concept 23.4: Natural selection is the only mechanism that consistently causes adaptive evolution Only natural selection consistently results in _________________________ evolution Relative _______________________ is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals Selection favors certain _______________________ by acting on the _________________________ of certain organisms Three modes of selection: o __________________________ selection favors individuals at one end of the phenotypic range o _________________________ selection favors individuals at both extremes of the phenotypic range o ___________________ selection favors intermediate variants and acts against extreme phenotypes Label the picture ____________________ selection is natural selection for mating success o It can result in sexual ________________________, marked differences between the sexes in secondary sexual characteristics ______________________ selection is competition among individuals of one sex (often males) for mates of the opposite sex ______________________ selection, often called mate choice, occurs when individuals of one sex (usually females) are choosy in selecting their mates ______________________ selection occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population _____________________________ advantage occurs when heterozygotes have a higher fitness than do both homozygotes o Natural selection will tend to ______________________ two or more alleles at that locus o The sickle-cell allele causes mutations in _____________________ but also confers malaria resistance In ________________________________ selection, the fitness of a phenotype declines if it becomes too common in the population o Selection can favor whichever phenotype is ___________ common in a population ___________________ variation is genetic variation that appears to confer no selective advantage or disadvantage o For example - Variation in ___________________ regions of DNA; Variation in proteins that have little effect on protein function or reproductive fitness Why Natural Selection Cannot Fashion Perfect Organisms 1. 2. 3. 4. Selection can _______ only on existing variations Evolution is _________________ by historical constraints Adaptations are often ____________________________ Chance, natural selection, and the environment _________________________ You should now be able to… 1. Explain why the majority of ______________ mutations are harmless 2. Explain how ________________ recombination generates genetic variability 3. Define the terms population, species, gene pool, relative fitness, and neutral variation 4. List the ______________ conditions of Hardy-Weinberg equilibrium 5. Apply the Hardy-Weinberg equation to a population genetics problem 6. Explain why natural selection is the ____________ mechanism that consistently produces adaptive change 7. Explain the ___________ of population size in genetic drift 8. Distinguish among the following sets of terms: directional, disruptive, and stabilizing selection; intrasexual and intersexual selection 9. List ____________ reasons why natural selection cannot produce perfect organisms