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Chapter 23: Problem 3

Define the following: (a) polygenic, (b) additive alleles, (c) correlation, (d) monozygotic and dizygotic twins, (e) heritability, (f) \(\mathrm{QTL},\) and \((\mathrm{g})\) continuous variation.

Short Answer

Expert verified
Question: Define heritability and explain why it is important in the study of genetics. Answer: Heritability is a measure of how much of the variability in a particular trait can be attributed to genetic factors as opposed to environmental factors. It is represented as a ratio ranging from 0 to 1, with 0 indicating that genetic factors do not contribute to the trait and 1 indicating that the trait is entirely determined by genetic factors. It is important in the study of genetics as it helps researchers determine the extent to which genetic factors influence a trait and identify the specific genes responsible for the variation in the trait.

Step by step solution

01

(a) Polygenic

A polygenic trait is a characteristic that is influenced by multiple genes. These genes, known as polygenes, each contribute to the overall trait in a small and often additive manner. Examples of polygenic traits include height, skin color, and intelligence.
02

(b) Additive alleles

Additive alleles are pairs of genes that contribute to a particular trait in an additive fashion. This means that the effects of each allele can be combined to determine the overall expression of a particular trait, such as height or intelligence. The presence of multiple additive alleles within the population can contribute to a continuous range of variation in a trait.
03

(c) Correlation

Correlation is a statistical measure that describes the strength and direction of a relationship between two continuous variables. Correlation ranges from -1 (strong negative relationship) to 1 (strong positive relationship), with 0 indicating no relationship. In the context of genetics, correlation can be used to assess the degree to which genetic factors influence a trait.
04

(d) Monozygotic and dizygotic twins

Monozygotic twins, also known as identical twins, are formed when a single fertilized egg splits into two embryos. These twins share virtually 100% of their genetic material, making them valuable for studying genetic influences on traits. Dizygotic twins, also known as fraternal twins, are formed when two separate eggs are fertilized by two different sperm cells. These twins share approximately 50% of their genetic material, like any siblings.
05

(e) Heritability

Heritability is a measure of how much of the variability in a particular trait can be attributed to genetic factors as opposed to environmental factors. It is represented as a ratio ranging from 0 to 1, with 0 indicating that genetic factors do not contribute to the trait and 1 indicating that the trait is entirely determined by genetic factors.
06

(f) QTL

QTL, or Quantitative Trait Locus, is a region on a chromosome that contains one or more genes associated with a quantitative trait. These traits exhibit continuous variation, and the genes within a QTL often have a cumulative effect on the trait. QTL mapping studies use statistical methods to identify the specific locations on chromosomes where these genes are located.
07

(g) Continuous variation

Continuous variation describes traits that exhibit a continuous range of values rather than discrete, distinct categories. Continuous traits often result from the combined influence of multiple genes. Examples of traits with continuous variation include height, blood pressure, and intelligence.

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Most popular questions from this chapter

Osteochondrosis (OC) is a developmental orthopedic disorder in young, growing horses, where irregular bone formation in the joints leads to necrotic areas, resulting in chronic or recurrent lameness. Incidence of OC varies considerably among breeds, and displays a multifactorial mode of inheritance. The incidence of \(\mathrm{OC}\) is rising in the population of race horses. Discuss the reasons why the incidence of OC might be rising, and describe what can be done to detect OC susceptibility in horses with the help of QTL analysis.

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 darkred: 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 symbols to these alleles and list possible 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.

Define the term broad-sense heritability \(\left(H^{2}\right) .\) What is implied by a relatively high value of \(H^{2}\) ? Express aspects of broad-sense heritability in equation form.

Many traits of economic or medical significance are determined by quantitative trait loci (QTLs) in which many genes, usually scattered throughout the genome, contribute to expression. (a) What general procedures are used to identify such loci? (b) What is meant by the term cosegregate in the context of QTL mapping? Why are markers such as RFLPs, SNPs, and microsatellites often used in QTL mapping?

The mean and variance of plant height of two highly inbred strains \(\left(P_{1} \text { and } P_{2}\right)\) and their progeny \(\left(F_{1} \text { and } F_{2}\right)\) are shown here. $$\begin{array}{ccc}\text { Strain } & \text { Mean (cm) } & \text { Variance } \\\\\mathrm{P}_{1} & 34.2 & 4.2 \\\\\mathrm{P}_{2} & 55.3 & 3.8 \\\\\mathrm{F}_{1} & 44.2 & 5.6 \\\\\mathrm{F}_{2} & 46.3 & 10.3\end{array}$$ Calculate the broad-sense heritability \(\left(H^{2}\right)\) of plant height in this species.
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