Download Answers to End-of-Chapter Questions – Brooker et al ARIS site

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 17
Test Yourself Questions
1. Quantitative traits such as height and weight are governed by several genes that usually contribute
in an additive way to the trait. This is called
a. independent assortment.
b. discontinuous inheritance.
c. maternal inheritance.
d. linkage.
e. polygenic inheritance.
Answer: e. The inheritance pattern of most quantitative traits is polygenic.
2. When two genes are located on the same chromosome they are said to be
a. homologous.
b. allelic.
c. epistatic.
d. linked.
e. polygenic.
Answer: d. Genes located on the same chromosome are said to be linked.
3. Based on the ideas proposed by Morgan, which of the following statements concerning linkage is not
true?
a. Traits determined by genes located on the same chromosome are likely to inherit together.
b. Crossing over between homologous chromosomes can create new gene combinations.
c. Crossing over is more likely to occur between genes that are closer together.
d. The probability of crossing over depends on the distance between the genes.
e. All but one of the above statements are correct.
Answer: c. Crossing over is less likely to occur between two genes that are closer together.
4. In genetic linkage mapping, one map unit is equivalent to
a. one hundred base pairs.
b. one base pair.
c. 10% recombination frequency.
d. 1% recombination frequency.
e. 1% the length of the chromosome.
Answer: d. One map unit, or centiMorgan, is equal to one percent recombination.
5. Organelle heredity is possible because
a. gene products may be stored in organelles.
b. mRNA may be stored in organelles.
c. some organelles contain genetic information.
d. conjugation of nuclei occurs before cellular division.
e. both a and c.
Answer: c. Some organelles, such as mitochondria and chloroplasts, possess DNA molecules with
functional genes.
6. In many organisms, organelles such as the mitochondria, are contributed by only the egg. This
phenomenon is known as
a. biparental inheritance.
b. paternal inheritance.
c. maternal effect.
d. maternal inheritance.
e. both c and d.
Answer: d. Maternal inheritance describes the pattern by which organelles are inherited only through the
egg.
7. Modification of a gene during gamete formation or early development that alters the way the gene is
expressed during the individual’s lifetime is called
a. maternal inheritance.
b. epigenetic inheritance.
c. epistasis.
d. multiple allelism.
e. alternative splicing.
Answer: b. Epigenetic inheritance describes events that occur before fertilization or in the early stages
of development that alter the way a gene will be expressed.
8. When a gene is inactivated during gamete formation and that gene is maintained in an inactivated
state in the somatic cells of offspring, such an inheritance pattern is called
a. linkage.
b. X inactivation.
c. maternal effect.
d. genomic imprinting.
e. polygenic inheritance.
Answer: d. Genomic imprinting is a phenomenon whereby the expression of a gene is dependent on
which parent transmits the gene.
9. Calico coat pattern in cats is the result of
a. X inactivation.
b. epistasis.
c. organelle heredity.
d. genomic imprinting.
e. maternal inheritance.
Answer: a. The calico pattern seen in cats and other animals is the result of X-inactivation in a female
that is heterozygous for coat color.
10. Maternal effect inheritance can be explained by
a. gene products that are given to an egg by the nurse cells.
b. the methylation of genes during gamete formation.
c. the spreading of X inactivation from the Xic locus.
d. the inheritance of alleles that contribute additively to a trait.
e. none of the above.
Answer: a. In maternal inheritance, the genotype of the mother determines the phenotype of the
offspring. This occurs because the diploid nurse cells provide the egg with their gene products.
Conceptual Questions
1. Define linkage and linkage group.
linkage: The phenomenon of two genes that are close together on the same chromosome tending to be
transmitted as a unit.
linkage group: A group of genes that usually stay together during meiosis.
2. Explain extranuclear inheritance and give two examples.
Answer: The transmission of genes that are located outside the cell nucleus is called extranuclear
inheritance. Two important types of extranuclear inheritance patterns involve genes that are found in
mitochondria and chloroplasts. The pigmentation of four o’clock plants involves the inheritance of genes
located in the chloroplasts and Leber’s Hereditary Optic Neuropathy in humans involves the inheritance
of mitochondrial genes.
3. Define genomic imprinting.
genomic imprinting: A phenomenon in which a segment of DNA is imprinted, or marked, in a way that
affects gene expression throughout the life of the individual who inherits that DNA.
Experimental Questions
1. What hypothesis were Bateson and Punnett testing when conducting the crosses in the sweet pea?
Answer: Bateson and Punnett were testing the hypothesis that the gene pairs that influence flower color
and pollen shape would assort independently of each other. The two traits were expected to show a
pattern consistent with Mendel’s law of independent assortment.
2. What were the expected results of Bateson and Punnett’s cross?
Answer: The expected results were a phenotypic ratio of 9:3:3:1. The researchers expected 9/16 of the
offspring would have purple flowers and long pollen, 3/16 of the offspring would have purple flowers and
round pollen, 3/16 of the offspring would have red flowers and long pollen and 1/16 of the offspring
would have red flowers and round pollen.
3. How did the observed results differ from the predicted results? How did Bateson and Punnett explain
the results of this particular cross?
Answer: Though all four of the expected phenotype groups were seen, they were not in the predicted
ratio of 9:3:3:1. The number of individuals with the phenotypes found in the parental generation (purple
flowers and long pollen or red flowers and round pollen) was much higher than expected. Bateson and
Punnett suggested that the gene controlling flower color were somehow coupled with the gene that
controls pollen shape. This would explain why these traits did not always assort independently.
Collaborative Questions
1. Discuss two types of gene interactions.
Answer:
Epistasis - this is when one gene prevents the expression of the dominant allele of another gene.
Epistasis often occurs because two or more different proteins are involved in a single cellular function.
As a result, one protein interferes with another which can sometimes lead to unexpected and
unpredictable results.
Polygenic inheritance - For most traits the phenotype cannot be sorted into discrete categories and are
said to be continuous and show a variation over a range of phenotypes. These traits are sometimes
referred to as quantitative traits which include, in humans, height, weight, skin color and metabolism.
Such continuous traits are polygenic in which several or many genes contribute to the outcome of the
trait.
2. Discuss the concept of linkage.
Answer: According to Mendel’s laws, alleles segregate independently of each other. But, this is not
always the case. Thomas Hunt Morgan proposed that genes located close to each other on the same
chromosome will be inherited as a group. This concept is known as linkage. Research has shown that
more offspring have similar parental combinations than would be predicted by independent assortment.
The reason for inheriting this parental combination is due to the fact that crossing-over has not occurred
between this set of genes and they are inherited as a unit. The closer two genes are to each other
(therefore the more closely linked they are) the less likely that they will be separated by crossing-over.
Conversely, the farther two genes are from each other the less linked they are and the more likely that
that they will be separated by crossing over.