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Chapter 20: Problem 3

Define the following: (a) polygenic, (b) additive alleles, (c) monozygotic and dizygotic twins, (d) heritability, and (e) QTL.

Short Answer

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Question: Define the following terms related to genetics: (a) polygenic, (b) additive alleles, (c) monozygotic and dizygotic twins, (d) heritability, and (e) QTL (Quantitative Trait Loci).

Step by step solution

01

(a) Polygenic

Polygenic refers to a trait or characteristic that is determined by the interaction of multiple genes, each of which individually contributes to the expression of the trait. These multiple genes together influence the trait, rather than being controlled by a single gene.
02

(b) Additive Alleles

Additive alleles are the different forms (variants) of a gene that have a cumulative or additive effect on a quantitative trait. The effect of each allele adds up, contributing to the overall phenotype of an individual. This is in contrast to non-additive effects, such as dominance or epistasis, where the influence of one allele may overshadow or interact with another allele's effect.
03

(c) Monozygotic and Dizygotic Twins

Monozygotic twins are identical twins that develop from a single fertilized egg (zygote) that splits into two embryos. These twins have nearly identical genetic makeup, as they share the same genes inherited from their parents. Dizygotic twins, also known as fraternal twins, develop from two separate fertilized eggs (zygotes) and have different genetic constitutions. These twins share only about 50% of their genes, just like regular siblings.
04

(d) Heritability

Heritability is a measure of the proportion of variation or differences in a particular trait among individuals within a population that can be attributed to genetic factors. It is expressed as a value between 0 and 1, where 0 indicates that none of the variation is due to genetics, and 1 denotes that all variation is due to genetic factors. It is important to note that heritability estimates apply to populations and not to individual organisms.
05

(e) QTL (Quantitative Trait Loci)

Quantitative Trait Loci (QTL) are specific regions of DNA where genetic variations are associated with the expression of a quantitative trait, such as height, weight, or blood pressure. QTLs may encompass multiple genes that contribute to the trait's variation. The mapping and identification of QTLs help in understanding the genetic basis of complex traits and diseases, which are influenced by multiple genes and environmental factors.

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Most popular questions from this chapter

A strain of plants has a mean height of \(24 \mathrm{cm} .\) A second strain of the same species from a different geographical region also has a mean height of \(24 \mathrm{cm}\). When plants from the two strains are crossed together, the \(F_{1}\) plants are the same height as the parent plants. However, the \(\mathrm{F}_{2}\) generation shows a wide range of heights; the majority are like the \(P_{1}\) and \(F_{1}\) plants, but approximately 4 of 1000 are only \(12 \mathrm{cm}\) high, and about 4 of 1000 are \(36 \mathrm{cm}\) high. (a) What mode of inheritance is occurring here? (b) How many gene pairs are involved? (c) How much does each gene contribute to plant height? (d) Indicate one possible set of genotypes for the original \(\mathrm{P}_{1}\) parents and the \(\mathrm{F}_{1}\) plants that could account for these results. (e) Indicate three possible genotypes that could account for \(\mathrm{F}_{2}\) plants that are \(18 \mathrm{cm}\) high and three that account for \(\mathrm{F}_{2}\) plants that are \(33 \mathrm{cm}\) high.

In a population of tomato plants, mean fruit weight is \(60 \mathrm{g}\) and \(\left(h^{2}\right)\) is \(0.3 .\) Predict the mean weight of the progeny if tomato plants whose fruit averaged 80 g were selected from the original population and interbred.

Height in humans depends on the additive action of genes. Assume that this trait is controlled by the four loci \(R, S, T,\) and \(U\) and that environmental effects are negligible. Instead of additive versus nonadditive alleles, assume that additive and partially additive alleles exist. Additive alleles contribute two units, and partially additive alleles contribute one unit to height. (a) Can two individuals of moderate height produce offspring that are much taller or shorter than either parent? If so, how? (b) If an individual with the minimum height specified by these genes marries an individual of intermediate or moderate height, will any of their children be taller than the tall parent? Why or why not?

List as many human traits as you can that are likely to be under the control of a polygenic mode of inheritance.

A dark-red strain and a white strain of wheat are crossed and produce an intermediate, medium-red \(\mathrm{F}_{1}\). When the \(\mathrm{F}_{1}\) plants are interbred, an \(\mathrm{F}_{2}\) generation is produced in a ratio of 1 dark-red: 4 medium-dark-red: 6 medium-red: 4 light-red: 1 white, Further crosses reveal that the dark-red and white \(\mathrm{F}_{2}\) plants are true breeding. (a) Based on the ratios in the \(\mathrm{F}_{2}\) population, how many genes are involved in the production of color? (b) How many additive alleles are needed to produce each possible phenotype? (c) Assign symhols to these alleles and list pnssible genotypes that give rise to the medium-red and light-red phenotypes. (d) Predict the outcome of the \(F_{1}\) and \(F_{2}\) generations in a cross between a true-breeding medium-red plant and a white plant.
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