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A.P. Biology Ch. 22
The Evolution of Populations
| Question | Answer |
|---|---|
| Microevolution | The process through which allele frequencies change within a population over generations. |
| Discrete Character | A character that can vary within a population and can be classified on an "either or" basis because it is determined by one locus with different alleles that produce distinctive phenotypes. |
| Quantitative Character | A character that can vary along a continuum within a population because it usually results from the influence of two or more genes on a single phenotypic character. |
| Average Heterozygosity | The average percent of loci that are heterozygous, which can quantify the gene variability of the population, but cannot detect silent mutations that alter the DNA sequence not the amino acid. |
| Geographic Variation | The differences in the genetic compositions of separate populations. |
| Cline | A graded change in a character along a geographic axis, which can be produced natural selection in response to a gradation in an environmental variable, for example, temperature. |
| Mutation | A change in the nucleotide sequence of an organism's DNA, which represents the ultimate source of new alleles within a population. |
| Point Mutation | A change in a single base within a gene, which can result in a different phenotype, for example, sickle cell disease. |
| How are gene duplications beneficial to the process of evolution? | If they do not have severe effects, they can persist over generations and allow mutations to accumulate, which results in an expanded genome with new loci that can take on new functions and make the organism better suited for its environment. |
| Population | A group of individuals that live in the same area and interbreed, producing fertile offspring. |
| Gene Pool | All the alleles for all the loci in all individuals of the population. |
| What are the two possible conditions of the alleles in the gene pool? | The alleles can be either fixed with one allele for each locus or "not fixed" with multiple alleles for each locus. |
| Hardy-Weinberg Principle | The frequencies of alleles and genotypes in a population will remain constant from generation to generation, if the gene pool remains in Hardy-Weinberg equilibrium. |
| Hardy-Weinberg Equilibrium | The state in which the gene pool is only altered through Mendelian segregation and the recombination of alleles. |
| Hardy-Weinberg Equation | p2 + 2pq + q2, where p2 is the expected frequency of the homozygous dominant genotype, 2pq is the expected frequency of the heterozygous genotype, and q2 is the expected frequency of the homozygous recessive genotype. |
| What are the five conditions required to use the Hardy-Weinberg Principle? | No mutations, random mating, no natural selection, extremely large population size, and no gene flow because all of these conditions prevent significant changes within the gene pool. |
| How can the Hardy-Weinberg Principle be applied in real life? | Some loci can be at Hardy-Weinberg equilibrium, while others can undergo substantial changes to the gene pool, and some populations evolve so slowly that changes to their allele and genotype frequencies they do not appear to have evolved. |
| Genetic Drift | The process that causes allele frequencies to fluctuate unpredictably from one generation to the next, thus, resulting in a loss of genetic variation within populations and the transformation of harmful to beneficial alleles. |
| Founder Effect | When a few individuals become indiscriminately isolated from a larger population, and the smaller group establishes a new population with a different gene pool than the original population; accounting for the high levels of inherited issues on islands. |
| Bottleneck Effect | When the population decreases rapidly due to natural selection, following a sudden environmental change, so the remaining population has overrepresented, underrepresented, and nonexistent alleles in the new gene pool and limited genetic variation. |
| Gene Flow | The transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes, which can result in the the introduction of new alleles into the population, as well as the direct alteration of the alleles. |
| Relative Fitness | The contribution of the individual to the gene pool of the next generation, relative to the contribution of other individuals. |
| Directional Selection | When the environment favors individuals exhibiting one extreme of a phenotypic range, which occurs due to part of the population migrating or a change in the habitat, so the frequency curve for the phenotypic character shifts in one direction. |
| Disruptive Selection | When the environment favors individuals at both extremes of the phenotypic range over individuals with intermediate phenotypes. |
| Stabilizing Selection | When the environment favors individuals with intermediate phenotypes over individuals with extreme phenotypes, thus reducing variation and maintaining the status quo for a particular phenotypic character. |
| How can adaptations arise from natural selection? | Natural selection increases the frequencies of alleles that enhance survival and reproduction, so the proportion of individuals that have favorable traits increases, the match between the species and the environment improves, and adaptations arise. |
| Sexual Selection | A form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates. |
| Sexual Dimorphism | The product of sexual selection that makes visible differentiations between the two sexes in secondary sexual characteristics that are not directly associated with reproduction or survival. |
| Intrasexual Selection | Individuals of one sex compete directly for mates of the opposite sex, resulting in natural selection among the same sex. |
| Intersexual Selection | Also known as mate choice, in which individuals of one sex select mates from the other sex based on the characteristics favored in the environment. |
| What prevents natural selection from reducing genetic variation by culling all unfavorable genotypes? | The tendency for directional and stabilizing selection to reduce variation is countered by mechanisms that preserve or restore it. |
| Diploidy | The condition of many eukaryotes that allows a considerable amount of genetic variation to be hidden from selection in the form of recessive alleles. |
| Balancing Selection | When natural selection maintains two or more forms in a population, including heterozygote advantage and frequency-dependent selection. |
| Heterozygote Advantage | When natural selection tends to maintain multiple alleles at one locus, so individuals that are heterozygous at the particular locus have a greater fitness than their homozygous counterparts. |
| Is heterozygote advantage an example of stabilizing or directional selection? | It depends on the relationship between the genotype and the phenotype, if the phenotype is intermediate to the homozygous phenotypes than it is stabilizing. |
| Frequency-Dependent Selection | The fitness of a phenotype declines if it becomes too common in the population. |
| Neutral Variation | When the nucleotide differences in noncoding sequences of DNA appear to confer no selective advantage or disadvantage, which can result from mutations and can change due to genetic drift. |
| Why can natural selection not produce perfect organisms? | It can only act on existing variations, it is limited by historical constraints, adaptations are often compromises, and chance interacts with natural selection and the environment. |
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