Chapter 23 Quantitative Genetics and Multifactorial Traits1) Quantitative inheritance involves the interaction of a number of gene loci. The pattern of genetic transmission typical of quantitative inheritance is ________.A) discontinuous distributions such as 3:1B) typical of Mendelian inheritanceC) continuous variation of phenotypic expressionD) a 9:3:3:1 ratioE) usually a pattern that clearly reflects dominance and recessivenessAnswer: CSection: 23.12) Assume that a cross is made between tall and dwarf tobacco plants. The F1 generation showedintermediate height, while the F2 generation showed a distribution of height ranging from tall to dwarf, like the original parents, and many heights between the extremes. These data are consistent with which one of the following modes of inheritance?A) multiple-factor inheritanceB) alternation of generationsC) codominanceD) incomplete dominanceE) hemizygosityAnswer: ASection: 23.1, 23.23) Bell-shaped distributions produced by plotting results of F2 and F3 crosses are typical of which type of inheritance?A) multiple-factor inheritanceB) alternation of generationsC) codominanceD) incomplete dominanceE) hemizygosityAnswer: ASection: 23.34) Characteristics exhibited by continuously varying traits include ________.A) sex-linked genes onlyB) autosomal genes onlyC) quantification by measuring, weighing, counting, etc.D) a 9:3:3:1 ratioE) 3:1 and 1:1 ratiosAnswer: CSection: 23.1, 23.2, 23.31Copyright © 2012 Pearson Education, Inc.5) Environmental factors typically influence inheritance of ________.A) multiple allelesB) codominanceC) trihybrid crossesD) polygenic traitsE) dominantly inherited traitsAnswer: DSection: 23.16) Huntington disease is inherited in humans as an autosomal dominant gene. Affected individuals show progressive brain deterioration from cell death in the cerebral cortex. Onset of the disease usually occurs between ages 30 and 50. Give two possible reasons for the observed variation in the age of onset of this disease.Answer: variable genetic background, internal physiological environment, external environmentSection: 22.37) In the analysis of quantitative traits, positions on chromosomes called quantitative trait loci (QTLs) are often discussed. In the same context, restriction fragment length polymorphisms (RFLPs) are also discussed. What is the relationship between QTLs and RFLPs?Answer: In many organisms, traditional genetic markers are not available for the mapping of regions of chromosomes containing genes responsible for determining quantitative traits (QTLs).DNA polymorphisms generate molecular markers (RFLPs), which can serve as reference points in mapping QTLs.Section: 23.68) List at least two statistical terms commonly used in the analysis of quantitative traits.Answer: mean, variance, standard deviation, standard error of the meanSection: 23.39) Define the term broad-sense heritability (H2). What is implied by a relatively high value of H2? Express aspects of broad-sense heritability in equation form.Answer: Broad-sense heritability (H2) refers to the degree to which phenotypic variation is due to genetic factors. A very high value indicates that the environment had a relatively low impact on phenotypic variation. VP = VE + VG + VGESection: 23.410) Describe the value of using twins in the study of questions relating to the relative impact of heredity versus environment.Answer: Monozygotic twins are derived from the splitting of a single fertilized egg and are therefore of identical genetic makeup. When such twins are raised in the same versus different settings, an estimate of relative hereditary and environmental influences can often be made.Section: 23.52Copyright © 2012 Pearson Education, Inc.11) In the early part of the twentieth century, Nilsson-Ehle and others described experiments showing that multiple loci may be involved in the inheritance of certain traits. Such patterns are often called ________.Answer: polygenic traits or multiple-factor inheritanceSection: 23.1, 23.212) If the proportion of F2 individuals resembling either of the two most extreme phenotypes (the parental phenotypes) can be determined, what formula can be applied to determine the number of gene pairs involved?Answer: 1/4n (where n is the number of gene pairs)Section: 23.213) What formula can be used to determine the number of categories (phenotypes) possible in theF2 results of a polygenic system?Answer: 2n + 1 (where n is the number of gene pairs)Section: 23.214) Assume that in the F2 of a series of crosses, 1/64 of the offspring resemble one of the parents(P). How many gene pairs are involved in producing these results?Answer: threeSection: 23.215) Assume that four polygenic gene pairs are involved in determining phenotypes of F2. How many phenotypic classes are expected?Answer: nineSection: 23.216) What is the term given to a random subset of individuals who are selected for measurement in a particular study?Answer: sampleSection: 23.317) When a trait is polygenic, but distinguished from continuous and meristic traits by having a small number of discrete classes, it is said to be a(n) ________ trait.Answer: thresholdSection: 23.118) List at least three statistical values often used to represent a sample.Answer: mean, standard deviation, standard error, varianceSection: 23.319) Given the following numbers, calculate the mean: 10, 12, 14, 16, 18.Answer: 14Section: 23.33Copyright © 2012 Pearson Education, Inc.20) What are the name and formula for describing sample variability?Answer: variance; s2 = S (Xi - X)2/n-1Section: 23.321) To estimate how much the means of a variety of like samples drawn from the same population might vary, what statistic is often used and what is the formula for it?Answer: standard error of the mean; (Sx = s/n)Section: 23.322) If one is attempting to determine the influence of genes or the environment on phenotypic variation, inbred strains with individuals of a relatively homogeneous or constant genetic background are often used. Variation observed between different inbred strains reared in a constant or homogeneous environment would likely be caused by genetic factors. What would bethe source of variation observed among members of the same inbred strain reared under varying environmental conditions?Answer: nongenetic factors generally categorized as "environmental"Section: 23.423) What is the formal expression used to examine the relative importance of genetic