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Exam 21: Genetic Analysis of Quantitative Traits

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Question 21

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A strain of a cereal grain can be either dark tan, medium-dark tan, medium tan, light tan, or cream colored. When a dark tan and a cream plant are crossed, all F₁ are medium tan. The F₂ are distributed in a ratio of 1:4:6:4:1 from darkest to lightest. How many genes are involved in this coloration?

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Question 22

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As an H² value approaches 0.0, which of the following must be true?

A) Almost all of the variation in phenotype is V_G.
B) Almost all of the variation in phenotype is V_E.
C) Identical (MZ) twins are virtually all discordant.
D) Fraternal (DZ) twins are virtually all concordant.
E) h² = V_A/V_P.

F) A) and E)
G) B) and E)

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Question 23

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An increased number of patients have recently been diagnosed with celiac disease, which you may know of as gluten sensitivity (OMIM 212750) . It is a multifactorial disorder of the small intestine influenced by genes and environment, and it is characterized by malabsorption due to inflammation of the mucosa after eating wheat gluten or related proteins. It is now thought to occur in 1 out of 120 to 300 people. Genes found to be associated with it are in the HLA region of chromosome 6, namely DR3 and DQw2. Which of the following is more probable?

Recent work in Drosophila demonstrated that the genes known as the chromatin remodeling complex co-localize at loci for hsp genes that respond to heat shock. Outline a procedure you could use to substantiate this finding.

For a specific desirable trait in a breed of sheep, V_P is 28.6, V_C is 11, and V_A is 7.2. What is its broad sense heritability?

Alterations in the ratio of CD4:CD8 lymphocytes are associated with risk of HIV infection progressing to AIDS, of autoimmune diseases, and of progression of some cancers. In searching for predictors of these effects in normal individuals, researchers have found two independent QTLs in the region of the genome known as the major histocompatibility complex (MHC) , one in a region regulating CD8 and the other in a region regulating CD4. What does this indicate for the general population?

Once a chromosomal position for a putative gene associated with Parkinson disease is verified, which of the following is a next step?

Given a list of concordances (as percentages)for monozygotic and dizygotic twins for a selection of traits, describe how you would evaluate the relative input of environmental versus genetic factors for each trait.

Sometimes the DNA marker allele and a QTL occur together more frequently than would otherwise be expected, either because they interact or because of natural selection. What term describes this?

Which of the following is most typical of a case of quantitative inheritance?

In some traits, different phenotypes result from genes whose alleles each contribute a specific increment to the whole. The phenotypes then have a ________ phenotypic distribution.

While most additive polygenic traits show continuous distribution, some can be divided into two or more categories based on their contribution to genetic liability. Such traits are said to have what separation between affected and unaffected members of a population?

What two measures describe the distribution of a trait in a sample?

If the odds ratio for a particular QTL/DNA marker pair (e.g., Q₁₀M₁₀)is 2.2, this indicates that the organism is how many times more likely to get Q₁₀M₁₀ gametes?

Many human behavioral traits have both genetic and environmental components. Bipolar disorder has long been known to be familial, and more recently a number of genes and/or SNPs have been found to be involved. What are three or more reasons that this research has been hampered?

An animal breeder asks your advice about which of a number of traits could most effectively be selected for in his herd. Which would you most correctly suggest?

Describe how quantitative traits can be explained in Mendelian terms.

A GWAS tests for a strong association of genotype (using DNA markers) and phenotype in natural populations. Therefore, which of the following would be true of linkage disequilibrium?

A strain of a cereal grain can be either dark tan, medium-dark tan, medium tan, light tan, or cream colored. When a dark tan and a cream plant are crossed, all F₁ are medium tan. The F₂ are distributed in a ratio of 1:4:6:4:1 from darkest to lightest. How many additive alleles are needed to produce the darkest phenotypes?

Which of the following best predicts the response of a trait to artificial selection?