# Mastering Biology Ch.23

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 Which of the following are basic components of the Hardy-Weinberg model? Frequencies of two alleles in a gene pool before and after many random matings. (Why: Hardy and Weinberg were trying to determine how and whether allele frequencies in a population change from one generation to the next. Which of the following statements is not a part of the Hardy-Weinberg principle? The genotype frequencies in the offspring generation must add up to two. (Why: This statement is not true; the genotype frequencies in the offspring generation must add up to one. True of false? The Hardy-Weinberg model makes the following assumptions: no selection at the gene in question; no genetic drift; no gene flow; no mutation; random mating. True (Why: these are 5 assumption of the Hardy-Weinberg model) What is the frequency of the A1A2 genotype in a population compose of 20 A1A1 individuals, A1A2 individuals, and 100 A2A2 individuals? 0.4 (Why: the calculation to determine the frequency of the A1A2 genotype is: 80 A1A2 individuals / (20+80+100) total individuals=0.4, the frequency of the A1A2 genotype. What is the frequency of the A1 allele in a population compose of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals? The frequency of the A1 allele is 0.3. (Why: the frequency of the A1 allele is p=(number of a1 alleles) / (total of all alleles) = [(2(20) + 80] / [(2 x 20) + (2 x 80) + (2 x100)]= 0.3 Which of the following evolutionary forces results in adaptive changes in allele frequencies? Selection (Why: selection is the only evolutionary force that consistently results in adaptation. Mutation without selection and genetic drift are random processes that may lead to adaptive, maladaptive, or neutral effects on populations.) What genotype frequencies are expected under Hardy-Weinberg equilibrium for a population with allele frequencies of p=0.8 and q=0.2 for a particular gene? The expected genotype frequencies are 0.64, 0.32, and 0.04 for A1A1, A1A2, and A2A2, respectively. (Why: the expected frequency of the A1A1 genotype is p^2=(0.8)(0.8)=0.64; the expected frequency of the A1A2 genotype is 2pq=2(0.8)(0.2)=0.32; the expected frequency of the A2A2 genotype is q^2=(0.2)(0.2)=0.4. To verify your calculations, confirm that the three frequencies add up to one. Which of the following evolutionary forces could create new genetic information in population? Mutation (Why: mutations, which are changes in a cell’s DNA, can introduce new genetic information in a population.) Generation-to-generation change in the allele frequencies in a population is _____. microevolution (Why: Generation-to-generation change in the allele frequencies in a population is the definition of microevolution) Which type of selection tends to increase genetic variation? Disruptive selection (Why: disruptive selection eliminates phenotypes near the average and favors the extreme phenotypes, resulting in increased genetic variation in a population.) In a bell-shaped curve, the x-axis (horizontal direction) of the graph represents which of the following? The value of a particular characteristic; characteristics of an organism can include such traits as size and color. (Why: the value of characteristics increases from left to right.) True or false? Heterozygote advantage refers to the tendency for heterozygous individuals to have better fitness than homozygous individuals. This higher fitness results in less genetic variation in the population. False (Why: Heterozygote advantage results in more genetic variation in the population.) Long necks make it easier for giraffes to reach leaves high on trees, while also making them better fighters in "neck wrestling" contests. In both cases, which kind of selection appears to have made giraffes the long-necked creatures they are today? Directional selection (Why: directional selection drives the average of the population in one direction, in this case, toward longer necks.) Women often have complication during labor while giving birth to very large babies, whereas very small babies tend to be underdeveloped. Which kind of selection is most likely at work regarding the birth weight of babies? Stabilizing selection (Why: Stabilizing selection causes no change in the average of the population; extreme phenotypes (in this case, large and small babies) become less common. Black-bellied seedcrackers have either small beaks (better for eating soft seeds) or large beaks (better for hard seeds). There are no seeds of intermediate hardness; therefore, which kind of selection acts on beak size in seedcrackers? Disruptive selection (Why: disruptive selection causes both extreme phenotypes (large and small beaks) to be favored over the intermediate phenotypes.) Small Aristelliger lizards have difficulty defending territories, but large lizards are more likely to be preyed upon by owls. Which kind of selection acts on the adult body size of these lizards? Stabilizing selection (Why: stabilizing selection causes no change in the average of population; extreme phenotypes (large and small lizards) become less common)

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