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Exam 24: Quantitative Genetics

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Question 31

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The estimated broad-sense heritability for milk production in a herd of dairy cattle is high. Which of the following statements is a valid inference?

A) Most of the variation in milk production in the herd is due to additive genetic variance within the herd.
B) Most of the variation in milk production in the herd is due to dominant genetic variance.
C) Little of the variation in milk production is due to environmental variation within the herd.
D) Selective breeding for high milk production in this herd will be effective.
E) Broad-sense heritability for milk production will be high in most other herds of dairy cattle.

F) D) and E)
G) A) and E)

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Question 32

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Cleft palate is a birth defect in which the two sides of the roof of the mouth do not fuse before birth. Cleft palate is considered to be a threshold trait. Define "threshold trait" and explain how cleft palate is an example of one.

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A threshold trait is a genetic trait tha...

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Question 33

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Phenotypic variation in tail length of unicorns has the following components: $\begin{array} { l | l | } \hline \text { Additive genetic variance } & = 0.2 \\\hline \text { Dominance genetic variance } & = 0.4 \\\hline \text { Genicinteraction variance } & = 0.1 \\\hline \text { Environmental variance } & = 0.2 \\\hline \text { Genetic-environmental interacti on variance } & = 0.5 \\\hline\end{array}$ What is the broad-sense heritability for tail length in these unicorns?

In a normal distribution, 99% of the measurements fall within:

Frankenstein tells Dracula that he thinks that fast-flying bats tend to suck blood faster than slow-flying bats do. Because flight speed is easier to measure than blood sucking is, Dracula considers how he might use this information in his breeding program. Could Dracula select on flight speed and get an increase in blood sucking? What information would Dracula need to be able to answer this question, and how might he determine this information?

Suppose that a study of college students in Sweden estimates heritability of IQ to be 0.8. Based on this evidence, a school board in a struggling urban school district in the United States concludes that improving teaching methods and the physical conditions of schools is useless because intellectual achievement is determined almost entirely by genes and relatively little by the educational environment. Critique this conclusion based on your understanding of heritability.

Cloning is a procedure by which exact genetic duplicates are made. A litter of cloned rabbits was born from a single surrogate mother rabbit. Despite being genetically identical, each of the baby rabbits looked very different from one another. Explain in detail why this might have occurred.

Two varieties-X (susceptible) and Y (resistant) -of eggplant were used to characterize the genetics of resistance to a necrotizing plant pathogen. Eight thousand plants from each variety were inoculated, and the average number of necrotic lesions produced per leaf was recorded. Variety X averaged 52 lesions per leaf, whereas variety Y averaged six lesions per leaf. The F₁ progeny from a cross between variety X and variety Y plants averaged 21 lesions per leaf, with a standard deviation of 3.7. Of the F₂ progeny, 8000 were again tested by inoculation, and a total of four plants produced were phenotypically similar to the original parental plants-two plants for each extreme (i.e., parental) phenotype. Overall, the F₂ plants averaged 18 lesions per leaf with a standard deviation of 7.5. -How many gene pairs control resistance to this pathogen?

Suppose that researchers estimate that broad-sense heritability of IQ in Sweden is 0.8. Which of the following conclusions is valid, assuming that the estimate is accurate?

The regression coefficient measures the _____ of the line depicting the relationship between two variables.

Use the following to answer questions The height of a type of bean plant is determined by five unlinked genes called A, B, C, D, and E. Each gene has two alleles: additive (uppercase letter) and nonadditive (lowercase letter). The shortest plants are 130 cm. The tallest plants are 220 cm. The genotypes are known for two bean plants. Plant 1 is genotype AABbccDdEE. Plant 2 is genotype aaBBCcDdEE. -a. Estimate how many centimeters each allele contributes to the height difference of 90 cm. b. The genotypes are known for two bean plants. Plant 1 is genotype AABbccDdEE. Plant 2 is genotype aaBBCcDdEE. What are their heights? c. If the two plants in the previous question are crossed, could they produce a plant that is taller than either parent? How? d. All the genes are unlinked. Determine the probability of an AbcdE gamete from plant 1 and an aBcdE gamete from plant 2. e. What will be the genotype and phenotype of a plant from these gametes, and what is the probability of a plant with this genotype? f. If the progeny plant from the cross in the previous question was only 60 cm because of an allele in a gene other than A-E, what genetic phenomena are at work? g. If the progeny plant with the genotype in part (d) was a few centimeters taller than your prediction, how would you explain it?

Suppose a new species of shark is discovered, and the dorsal fin length is found to be determined by additive alleles at three independently assorting loci (A and a, B and b, C and c) . The dorsal fin length of aabbcc sharks is 12 cm and the dorsal fin length of AABBCC sharks is 30 cm. Assuming that the alleles contribute equally, which of the following genotypes would represent a shark with a dorsal fin length of 18 cm?

Use the following to answer questions The height of a type of bean plant is determined by five unlinked genes called A, B, C, D, and E. Each gene has two alleles: additive (uppercase letter) and nonadditive (lowercase letter) . The shortest plants are 130 cm. The tallest plants are 220 cm. The genotypes are known for two bean plants. Plant 1 is genotype AABbccDdEE. Plant 2 is genotype aaBBCcDdEE. -If these two plants are crossed, could they produce a plant that is taller than either parent? How?

Phenotypic correlation may be due to genetic correlations such as _____, which is when one gene influences two or more traits.

_____ is a way to measure the strength of the association between two variables.

Use the following to answer questions The height of a type of bean plant is determined by five unlinked genes called A, B, C, D, and E. Each gene has two alleles: additive (uppercase letter) and nonadditive (lowercase letter) . The shortest plants are 130 cm. The tallest plants are 220 cm. The genotypes are known for two bean plants. Plant 1 is genotype AABbccDdEE. Plant 2 is genotype aaBBCcDdEE. -What are their heights?

In a group of 10 black bears, the length of the longest claw was measured in each bear. These lengths are listed below in cm. What is the variance of these lengths? 2.8, 3.1, 3.8, 3.2, 3.3, 2.9, 3.2, 3.1, 3.5, 3.0

Use the following to answer questions The height and weight for three dogs are shown below. $\begin{array}{cc}Weight~ in ~kilograms&Height~ in~ centimeters\\7 & 22 \\4 & 12 \\10 & 30\end{array}$ -What is the value of the correlation coefficient?

A series of experiments shows that oil content in a diploid grain is influenced by five genes (a through e) with additive alleles. The highest-producing strain has 20% oil content; the lowest has close to 0%. A plant of unknown genotype has an oil content of 12%. What is a possible genotype for this plant (+ = additive alleles) ?

Two highly inbred tobacco plants are crossed. One has dark green leaves. The other has yellow leaves. The F₁ have light green leaves. Five hundred progeny from F₁ × F₁ crosses are analyzed. Their leaves show continuous variation in color, but none has dark green or yellow leaves. What do these data suggest about the number of genes determining this trait?