Exam 21: Quantitative Genetics and Multifactorial Traits

Inbred strains with individuals of a relatively homogeneous or constant genetic background are often used to determine the influence of genes or the environment on phenotypic variation. 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 varying environmental conditions?

Bell -shaped distributions produced by plotting results of F2 and F3 crosses are typical of which type of inheritance?

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

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

A "marker" in a genetic sense usually represents a site along a chromosome where a specific nucleotide sequence exists. Which specific phrase is used when such markers are identified by restriction endonucleases and a particular set of DNA fragments is generated?

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 is meant by the term heritability? Describe the components of heritability and provide a brief explanation of each. Of what interest is heritability to animal and plant breeders?

Additive alleles are those that are epistatic over nonallelic genes that influence the same phenotypic characteristic.

What is the relationship between the narrow -sense heritability (h2) index and the impact of selection?

Given the following numbers, calculate the mean: 10, 12, 14, 16, 18.

The multiple -factor hypothesis suggests that many factors or genes contribute to the phenotype in a cumulative or quantitative manner.

To estimate how much the means of a variety of like samples drawn from the same population might vary, which statistic is often used and what is its formula?

Assume that a cross is made between tall and dwarf tobacco plants. The F1 generation showed intermediate height, whereas the F2 generation showed a distribution of height ranging from tall to dwarf, like the original parents, and many heights between the extremes. These data are consistent with which one of the following modes of inheritance?

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

Describe the value of using twins in the study of questions relating to the relative impact of heredity versus environment.

The 9:3:3:1 ratio is typical of a dihybrid cross in which complete dominance and independent assortment occur. What is the dihybrid ratio with independent assortment of polygenes?

Continuous inheritance is often related to the term quantitative inheritance. Why?

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

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

Characteristics exhibited by continuously varying traits include _.