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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

In a cross between a strain of large guinea pigs and a strain of small guinea pigs, the \(F_{1}\) are phenotypically uniform, with an average size about intermediate between that of the two parental strains. Among $1014 \mathrm{F}_{2}$ individuals, 3 are about the same size as the small parental strain and 5 are about the same size as the large parental strain. How many gene pairs are involved in the inheritance of size in these strains of guinea pigs?

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?

In an assessment of learning in Drosophila, flies were trained to avoid certain olfactory cues. In one population, a mean of 8.5 trials was required. A subgroup of this parental population that was trained most quickly (mean \(=6.0\) ) was interbred, and their progeny were examined. These flies demonstrated a mean training value of \(7.5 .\) Calculate realized heritability for olfactory learning in Drosophila.

In a herd of dairy cows the narrow-sense heritability for milk protein content is \(0.76,\) and for milk butterfat it is \(0.82 .\) The cor- relation coefficient between milk protein content and butterfat is \(0.91 .\) If the farmer selects for cows producing more butterfat in their milk, what will be the most likely effect on milk protein content in the next generation?

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