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Chapter 28
Genetics- Exam 2- Fall 2026
| Question | Answer |
|---|---|
| What is quantitative genetics? | The study of traits that can be described numerically. |
| What are complex traits? | Traits usually controlled by more than one gene and significantly influenced by environmental factors. |
| Give two examples of complex traits from the slides | Height and metabolic rate. |
| Why is quantitative genetics important to breeders? | Many key characteristics considered by plant and animal breeders are quantitative traits. |
| How can genes influence human disease? | Many human diseases are influenced by several genes. |
| How can quantitative traits aid adaptation? | Many traits that allow a species to adapt to its environment are quantitative traits. |
| What is a quantitative trait? | Any trait that varies measurably within a given species. |
| How may quantitative traits be measured? | Numerically, such as weight in kilograms, speed in km/h, or glucose burned per minute. |
| Can behavioral traits be quantitative? | Yes. For example, the duration and pattern of a mating call can be measured. |
| What is a continuous trait? | A trait that varies along a continuum rather than falling into discrete categories. |
| What is a meristic trait? | A trait expressed in whole-number counts, such as the number of bristles on a Drosophila back. |
| What is a discontinuous trait? | A trait that falls into two or more distinct categories. |
| Give an example of a discontinuous trait from the slides. | White or red eyes in fruit flies. |
| What is continuous variation? | A range of phenotypes within a group that cannot naturally be sorted into a small number of discrete categories. |
| What is a frequency distribution? | A way to describe quantitative variation by dividing a trait's range into phenotypic categories and counting individuals in each. |
| How were student heights categorized in the slide example? | The range of heights was partitioned into one-inch intervals. |
| What is a normal distribution? | A symmetrical, bell-shaped distribution in which values vary around an average. |
| What is the typical shape of many quantitative-trait distributions? | Approximately symmetrical and bell-shaped, resembling a normal distribution. |
| What is polygenic inheritance? | Transmission of traits governed by two or more genes. |
| How do most quantitative traits behave? | They are polygenic and exhibit a continuum of phenotypic variation. |
| What is a quantitative trait locus (QTL)? | A chromosomal location or region that affects the outcome of a quantitative trait. |
| What can a QTL contain? | One or more genes. |
| How are QTLs identified? | They are chromosomal regions identified through gene mapping. |
| What did Kolreuter observe when crossing tall and dwarf tobacco plants? | The F1 plants were intermediate in height, and the F2 generation showed a broad distribution of heights. |
| What did Kolreuter's tobacco experiment suggest? | A trait showing continuous variation could be inherited through multiple factors, although he did not understand the significance at the time. |
| Who demonstrated continuous variation related to polygenic inheritance in wheat in 1909? | Herman Nilsson-Ehle. |
| What wheat trait did Nilsson-Ehle study? | Red pigment in the hull of wheat, Triticum aestivum. |
| What happened when true-breeding red wheat was crossed with true-breeding white wheat? | The F1 generation had intermediate-red hulls; the F2 showed wide variation in redness, including white. |
| What is the multiple-gene or multiple-factor hypothesis? | The hypothesis that many genes or factors contribute quantitatively to a phenotype. |
| According to the hypothesis, how many genes influence the hereditary component? | At least two genes contribute to the phenotype in an additive way. |
| What does additive gene action mean in the slides' model? | The contributions of additive alleles at different loci accumulate to influence the phenotype. |
| What assumption does the model make about additive alleles at each locus? | Their effects are equivalent. |
| What dominance assumption is made by the simple multiple-factor model? | No allelic pair exhibits dominance of one allele over the other. |
| What assumption does the model make about interactions between loci? | No gene interactions occur among alleles at different loci in the polygenic series. |
| What linkage assumption does the model make? | The genes in the polygenic series are not genetically linked. |
| In the wheat hull-color example, what do A and B represent? | Two gene loci whose additive alleles contribute to red pigment. |
| What is the genotype of the true-breeding red parent in the wheat example? | AABB. |
| What is the genotype of the true-breeding white parent in the wheat example? | aabb. |
| What is the F1 genotype from AABB × aabb? | AaBb. |
| Why do F2 wheat hull colors form a range? | Different F2 genotypes carry different numbers of additive red alleles. |
| What F2 phenotypic ratio is shown for the two-gene wheat hull-color example? | 1:4:6:4:1, from the most red to the white extreme. |
| How many additive alleles are present in AABB? | Four; this produces the reddest phenotype in the example. |
| How many additive red alleles are present in aabb? | Zero; this produces the white phenotype in the example. |
| What phenotype is associated with AABB in the slide table? | Red |
| What phenotype is associated with AABB in the slide table? | White |
| What phenotype is associated with AABb or AaBB? | Dark pink |
| What phenotype is associated with AAbb, AaBb, or aaBB? | Medium pink |
| What phenotype is associated with Aabb or aaBb? | Light pink |
| Why is quantitative-trait analysis difficult? | Multiple genes control the traits, and environmental factors can substantially affect the phenotype. |
| How can the environment affect seed weight? | Environmental conditions can cause individuals with the same genotype to produce seeds of different weights. |
| How does one gene with little environmental variation affect genotype–phenotype matching? | The three genotypes can fall into distinct, non-overlapping phenotypic categories. |
| What happens when environmental variation increases for a one-gene trait? | Phenotypic ranges of different genotypes can overlap, making genotype harder to infer. |
| How does having three genes affect overlap between genotypes and phenotypes? | It creates more phenotypic classes and can make genotype identification more difficult, especially when environmental effects are substantial. |
| What is the F2 phenotypic ratio for one gene pair in the heterozygote cross described? | 1:2:1. |
| What F2 phenotypic ratio is given for three gene pairs in the slide example? | 1:6:15:20:15:6:1. |
| How is the proportion of individuals at either extreme in the F2 related to the number of gene pairs? | The ratio for either extreme phenotype is 1/4ⁿ, where n is the number of gene pairs involved. |
| How can the number of gene pairs be estimated from an extreme-phenotype proportion? | Use the relationship that the proportion at either extreme is 1/4ⁿ and solve for n. |
| How many distinct F2 phenotypic classes are predicted by the model? | 2n + 1, where n is the number of gene pairs. |
| What is the expected number of F2 phenotypic classes for two gene pairs? | 2(2) + 1 = 5 classes. |
| What is the expected number of F2 phenotypic classes for three gene pairs? | 2(3) + 1 = 7 classes. |
| What is the main distinction between genotype and phenotype in quantitative genetics? | Genotype is the genetic makeup; phenotype is the observable trait, which can also be influenced by the environment. |
Created by:
KristenR2025