Question 1

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.

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Question 2

You and a close friend from the University of Tennessee go hiking in the mountains.You are surprised to see a salamander that is bright orange in color.Thinking that some overzealous Tennessee fans have painted this particular amphibian, you walk on.As you continue your hike, you find other salamanders of this species and note that there is variation in the coloration: some individuals are bright orange, but others are drab in color.You also note that these salamanders often eat bright orange insects.How might you explain the presence of the color polymorphism in this salamander species?

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Question 3

Is it possible for a trait to be discontinuous and yet determined by multiple genetic and environmental factors? Explain.

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Question 4

In wheat, kernel color is determined by additive alleles at two unlinked loci.If two plants, with red kernels, heterozygous at both loci, are crossed, what fraction of the offspring is expected to have phenotypes distinct from parental?

Accepted Answer

In a dihybrid cross where both parents are heterozygous at two loci (AaBb x AaBb), the offspring can have a variety of genotypes. The phenotypes distinct from the parental phenotype occur when the offspring inherit either recessive alleles at both loci (aabb) or a combination that does not resemble the parent's dominant phenotype (e.g., AAbb, aaBB, Aabb, aaBb, AaBb). Using a Punnett square, you can calculate that 6/16 will have the same phenotype as the parents (A-B-), and 10/16 will have phenotypes distinct from the parents, including the fully recessive phenotype (aabb) and combinations thereof.

Question 5

Do the principles discovered by Mendel for discontinuous traits also apply to the inheritance of traits that exhibit continuous variation? Explain your answer.

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Question 6

Total phenotypic variance can be broken down into all but one of which of the following components?

Accepted Answer

Total phenotypic variance can be broken down into three components: genetic variance, environmental variance, and the variance due to their interaction (genetic-environment interaction variance). Heritability is not one of the components of total phenotypic variance but is a measure of the proportion of phenotypic variance that is due to genetic factors.

Question 7

Recently, genome-wide association studies that locate genes influencing quantitative traits have been facilitated by the use of:

Accepted Answer

Genome-wide association studies use single nucleotide polymorphisms (SNPs) to locate genes that influence quantitative traits. SNP genotyping technology has advanced significantly in recent years, allowing for high-throughput analysis of large numbers of SNPs across the genome. Pedigrees, controlled crosses, and clonal lineages can all be useful for studying the inheritance of traits and identifying the genetic basis of variation, but these approaches are not as well-suited for genome-wide association studies. Restriction fragment length polymorphisms (RFLPs) were an early marker type used for genetic mapping, but these have largely been replaced by SNPs due to the higher density of SNP markers and ease of genotyping.

Question 8

The model which best explains the inheritance of complex traits, such as height, weight, and IQ, attributes the control of the traits to:

Accepted Answer

Complex traits such as height, weight, and IQ are controlled by more than one gene, referred to as polygenic inheritance. Environmental factors can also have an impact on these traits. Therefore, the model that best explains the inheritance of complex traits is more than one gene plus environmental effects. Choice A is incorrect because complex traits are not controlled by a single gene with dominant and recessive alleles. Choice B is incorrect because complex traits are not controlled by two genes with independent assortment. Choice C is incorrect because complex traits are not controlled by more than one gene with no effect of the environment. Choice E is incorrect because genetic factors do play a role in the inheritance of complex traits.

Question 9

In wheat, kernel color is determined by additive alleles at two unlinked loci.If two plants, one with dark red kernels (+++- genotype), and one with light red kernels (+- - - genotype), are crossed, what fraction of the offspring is expected to have phenotypes distinct from parental colors?

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Question 10

A population may eventually stop responding to artificial selection because:

Accepted Answer

When individuals in the population become homozygous for the alleles responsible for the trait being selected, further response to artificial selection would be difficult because there is no genetic variation to select for. In addition, natural selection may oppose any further change in the characteristic if it is not beneficial for survival and reproduction. Therefore, D is the best choice because it combines these two factors.

Question 11

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.

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Question 12

In wheat, kernel color is determined by additive alleles at two unlinked loci.If two plants with red kernels, heterozygous at both loci, are crossed, what fraction of the offspring is expected to have phenotypes the most distinct from parental color?

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Question 13

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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Question 14

Estimates of heritability made by comparing related individuals assume that the environments of related individuals:

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Estimates of heritability that are made by comparing related individuals assume that the environments of related individuals are not any more similar than those in which unrelated individuals are raised. This assumption is necessary to isolate the genetic contribution to traits by minimizing the confounding effects of environmental similarities.

Question 15

A certain disease phenotype is a threshold trait, where disease occurs only if the number of susceptibility alleles in a genotype exceeds 3.How many phenotypic categories can be observed if the number of quantitative susceptibility loci has been determined as 5?

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Question 16

The graph below shows how yield in two varieties of corn respond to different environmental conditions.Which statement below is TRUE?

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Question 17

Genetic variance is comprised of all of the following components EXCEPT:

Accepted Answer

Broad-sense heritability is a measure that includes all genetic variance components (additive, dominance, and genic interaction) rather than being a component itself.

Question 18

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.
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.What will be the genotype and phenotype of a plant from these gametes, and what is the probability of a plant with this genotype?
e.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?
f.If the progeny plant with the genotype in part (d)was a few centimeters taller than your prediction, how would you explain it?

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Question 19

_____ measures the effect of alleles at a locus interacting in a non-additive fashion.

Accepted Answer

Dominance genetic variance measures the effect of alleles at a locus interacting in a non-additive fashion. This type of variance is separate from additive genetic variance which measures the individual effect of each allele without considering their interaction.

Question 20

A study was conducted to investigate the levels of calcium and growth hormone excreted in chicken dung on a major chicken farm.The variances (V)were calculated and are shown below.  a.Calculate the narrow-sense heritability for both traits (calcium and growth hormone levels).
b.Which trait, if any, will most likely respond to artificial selection?

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Quiz 17: Quantitative Genetics