Exam 23: Quantitative Genetics and Multifactorial Traits

Individuals with the same genetic background and a high degree of homozygosity are said to be isogenic. Of what value are isogenic strains in genetic studies?

Quantitative inheritance involves the interaction of a number of gene loci. The pattern of genetic transmission typical of quantitative inheritance is ________.

Heritability is a measure of the degree to which the phenotypic variation of a given trait is due to genetic factors.

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?

Traits such as height, general body structure, skin color, and some behavioral traits are probably caused primarily by genes that behave codominantly or epistatically.

Provide a brief description of discontinuous inheritance and continuous inheritance. How are the two related? How are they different?

List at least two statistical terms commonly used in the analysis of quantitative traits.

What formula can be used to determine the number of categories (phenotypes) possible in the F₂ results of a polygenic system?

Provide a brief definition of the terms additive variance, dominance variance, and interactive variance.

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 ________.

How would the use of a large series of monozygotic and dizygotic twins enhance studies on the genetic basis of human behavior?

Name two mammalian traits with relatively high heritability (h²) values and two with relatively low h² values.

What is the formal expression used to examine the relative importance of genetic versus environmental factors?

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?

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?

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.

What are QTLs and RFLPs?

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 be the source of variation observed among members of the same inbred strain reared under various environmental conditions?

What are the name and formula for describing sample variability?

Assume that four polygenic gene pairs are involved in determining phenotypes of F₂. How many phenotypic classes are expected?