Exam 25: Quantitative Genetics and Multifactorial Traits

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

Assume that a cross is made between tall and dwarf tobacco plants.The F₁ generation showed intermediate height,while 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?

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

Which theory suggests that many factors or genes contribute to the phenotype in a cumulative or quantitative manner?

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?

Define the term broad- sense heritability H².What is implied by a relatively high value of H²? Express aspects of broad- sense heritability in equation form.

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?

As used in twin studies in mammals,distinguish between the terms concordant and discordant.

When multiple genes contribute to the expression of a phenotype they are called _____ .

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?

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 QTLs?

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?

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

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

Interpret the meaning of an H² broad- sense heritability value that approaches 1.0.

What is the name of the process of selecting a specific group of organisms from an initially heterogeneous population for future breeding purposes?

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?

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

Polygenic traits often demonstrate a _____distribution when the phenotypes from a proper sample are represented in a histogram.