Question 1

SRY is best described in which of the following ways?

Accepted Answer

A)  a gene present on the X chromosome that triggers female development 
B)  an autosomal gene that is required for the expression of genes on the Y chromosome 
C)  a gene region present on the Y chromosome that triggers male development 
D)  an autosomal gene that is required for the expression of genes on the X chromosome 
E)  a gene required for development, and males or females lacking the gene do not survive past early childhood 
A)  a gene present on the X chromosome that triggers female development 
B)  an autosomal gene that is required for the expression of genes on the Y chromosome 
C)  a gene region present on the Y chromosome that triggers male development 
D)  an autosomal gene that is required for the expression of genes on the X chromosome 
E)  a gene required for development, and males or females lacking the gene do not survive past early childhood

Question 2

Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons?

Accepted Answer

A)  The frequency of crossing over varies along the length of the chromosome. 
B)  The relationship between recombination frequency and map units is different in every individual. 
C)  Physical distances between genes change during the course of the cell cycle. 
D)  The gene order on the chromosomes is slightly different in every individual. 
E)  Linkage map distances are identical between males and females. 
A)  The frequency of crossing over varies along the length of the chromosome. 
B)  The relationship between recombination frequency and map units is different in every individual. 
C)  Physical distances between genes change during the course of the cell cycle. 
D)  The gene order on the chromosomes is slightly different in every individual. 
E)  Linkage map distances are identical between males and females.

Question 3

In 1956 Tijo and Levan first successfully counted human chromosomes. What is the reason it took so many years to do so?

Accepted Answer

A)  Watson and Crick's structure of DNA was not done until 1953. 
B)  Chromosomes were piled up on top of one another in the nucleus. 
C)  Chromosomes were not distinguishable during interphase. 
D)  A method had not yet been devised to halt mitosis at metaphase. 
E)  Chromosomes were piled up on top of one another in the nucleus, chromosomes were not distinguishable during interphase, and a method had not yet been devised to halt mitosis at metaphase. 
A)  Watson and Crick's structure of DNA was not done until 1953. 
B)  Chromosomes were piled up on top of one another in the nucleus. 
C)  Chromosomes were not distinguishable during interphase. 
D)  A method had not yet been devised to halt mitosis at metaphase. 
E)  Chromosomes were piled up on top of one another in the nucleus, chromosomes were not distinguishable during interphase, and a method had not yet been devised to halt mitosis at metaphase.

Question 4

An inversion in a human chromosome often results in no demonstrable phenotypic effect in the individual. What else may occur?

Accepted Answer

A)  There may be deletions later in life. 
B)  Some abnormal gametes may be formed. 
C)  There is an increased frequency of mutation. 
D)  All inverted chromosomes are deleted. 
E)  The individual is more likely to get cancer. 
A)  There may be deletions later in life. 
B)  Some abnormal gametes may be formed. 
C)  There is an increased frequency of mutation. 
D)  All inverted chromosomes are deleted. 
E)  The individual is more likely to get cancer.

Question 5

A phenotypically normal prospective couple seeks genetic counseling because the man knows that he has a translocation of a portion of his chromosome 4 that has been exchanged with a portion of his chromosome 12. Although he is normal because his translocation is balanced, he and his wife want to know the probability that his sperm will be abnormal. What is your prognosis regarding his sperm?

Accepted Answer

A)  1/4 will be normal, 1/4 will have the translocation, and 1/2 will have duplications and deletions. 
B)  All will carry the same translocation as the father. 
C)  None will carry the translocation since abnormal sperm will die. 
D)  His sperm will be sterile and the couple might consider adoption. 
E)  1/2 will be normal and the rest will have the father's translocation. 
A)  1/4 will be normal, 1/4 will have the translocation, and 1/2 will have duplications and deletions. 
B)  All will carry the same translocation as the father. 
C)  None will carry the translocation since abnormal sperm will die. 
D)  His sperm will be sterile and the couple might consider adoption. 
E)  1/2 will be normal and the rest will have the father's translocation.

Question 6

Refer to the following information to answer the questions below.
A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was 6 feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive.
-What proportion of their sons would be color-blind and of normal height?

Accepted Answer

A)  none 
B)  half 
C)  one out of four 
D)  three out of four 
E)  all 
A)  none 
B)  half 
C)  one out of four 
D)  three out of four 
E)  all

Question 7

A certain kind of snail can have a right-handed direction of shell coiling (D)or left-handed coiling (d). If direction of coiling is due to a protein deposited by the mother in the egg cytoplasm, then a Dd egg-producing snail and a dd sperm-producing snail will have offspring of which genotype(s)and phenotype(s)?

Accepted Answer

A)  1/2 Dd:1/2 dd; all right coiling 
B)  all Dd; all right coiling 
C)  1/2 Dd:1/2 dd; half right and half left coiling 
D)  all Dd; all left coiling 
E)  all Dd; half right and half left coiling 
A)  1/2 Dd:1/2 dd; all right coiling 
B)  all Dd; all right coiling 
C)  1/2 Dd:1/2 dd; half right and half left coiling 
D)  all Dd; all left coiling 
E)  all Dd; half right and half left coiling

Question 8

When Thomas Hunt Morgan crossed his red-eyed F₁ generation flies to each other, the F₂ generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?

Accepted Answer

A)  The gene involved is on the Y chromosome. 
B)  The gene involved is on the X chromosome. 
C)  The gene involved is on an autosome, but only in males. 
D)  Other male-specific factors influence eye color in flies. 
E)  Other female-specific factors influence eye color in flies. 
A)  The gene involved is on the Y chromosome. 
B)  The gene involved is on the X chromosome. 
C)  The gene involved is on an autosome, but only in males. 
D)  Other male-specific factors influence eye color in flies. 
E)  Other female-specific factors influence eye color in flies.

Question 9

Use the following information to answer the questions below.
A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine as follows:
A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type):
  
-The greatest distance among the three genes is between a and c. What does this mean?

Accepted Answer

A)  Gene a is closest to b. 
B)  Genes are in the order: a-b-c. 
C)  Gene a is not recombining with c. 
D)  Gene a is between b and c. 
E)  Distance a-b is equal to distance a-c. 
A)  Gene a is closest to b. 
B)  Genes are in the order: a-b-c. 
C)  Gene a is not recombining with c. 
D)  Gene a is between b and c. 
E)  Distance a-b is equal to distance a-c.

Question 10

Women (and all female mammals)have one active X chromosome per cell instead of two. What causes this?

Accepted Answer

A)  modification of the XIST gene so that it is active only on one X chromosome, which then becomes inactive 
B)  activation of the Barr gene on one of the two X chromosomes that then inactivates 
C)  crossover between the XIST gene on one X chromosome and a related gene on an autosome 
D)  inactivation of the XIST gene on the X chromosome derived from the male parent 
E)  the removal of methyl (CH₃) groups from the X chromosome that will remain active 
A)  modification of the XIST gene so that it is active only on one X chromosome, which then becomes inactive 
B)  activation of the Barr gene on one of the two X chromosomes that then inactivates 
C)  crossover between the XIST gene on one X chromosome and a related gene on an autosome 
D)  inactivation of the XIST gene on the X chromosome derived from the male parent 
E)  the removal of methyl (CH₃) groups from the X chromosome that will remain active

Question 11

Which of the following is the meaning of the chromosome theory of inheritance as expressed in the early 20th century?

Accepted Answer

A)  Individuals inherit particular chromosomes attached to genes. 
B)  Mendelian genes are at specific loci on the chromosome and in turn segregate during meiosis. 
C)  Homologous chromosomes give rise to some genes and crossover chromosomes to other genes. 
D)  No more than a single pair of chromosomes can be found in a healthy normal cell. 
E)  Natural selection acts on certain chromosome arrays rather than on genes. 
A)  Individuals inherit particular chromosomes attached to genes. 
B)  Mendelian genes are at specific loci on the chromosome and in turn segregate during meiosis. 
C)  Homologous chromosomes give rise to some genes and crossover chromosomes to other genes. 
D)  No more than a single pair of chromosomes can be found in a healthy normal cell. 
E)  Natural selection acts on certain chromosome arrays rather than on genes.

Question 12

In humans, clear gender differentiation occurs, not at fertilization, but after the second month of gestation. What is the first event of this differentiation?

Accepted Answer

A)  formation of testosterone in male embryos 
B)  formation of estrogens in female embryos 
C)  anatomical differentiation of a penis in male embryos 
D)  activation of SRY in male embryos and masculinization of the gonads 
E)  activation of SRY in females and feminization of the gonads 
A)  formation of testosterone in male embryos 
B)  formation of estrogens in female embryos 
C)  anatomical differentiation of a penis in male embryos 
D)  activation of SRY in male embryos and masculinization of the gonads 
E)  activation of SRY in females and feminization of the gonads

Question 13

Three genes at three loci are being mapped in a particular species. Each has two phenotypes, one of which is markedly different from the wild type. The unusual allele of the first gene is inherited with either of the others about 50% of the time. However, the unusual alleles of the other two genes are inherited together 14.4% of the time. Which of the following describes what is happening?

Accepted Answer

A)  The genes are showing independent assortment. 
B)  The three genes are linked. 
C)  The first gene is linked but the other two are not. 
D)  The first gene is assorting independently from the other two that are linked. 
E)  The first gene is located 14.4 units apart from the other two. 
A)  The genes are showing independent assortment. 
B)  The three genes are linked. 
C)  The first gene is linked but the other two are not. 
D)  The first gene is assorting independently from the other two that are linked. 
E)  The first gene is located 14.4 units apart from the other two.

Question 14

Thomas Hunt Morgan's choice of Drosophila melanogaster has been proven to be useful even today. Which of the following has/have continued to make it a most useful species?
I.its four pairs of chromosomes
II.a very large number of visible as well as biochemically mutant phenotypes
III.easy and inexpensive maintenance
IV.short generation time and large number of offspring

Accepted Answer

A)  I and IV only 
B)  II and III only 
C)  I, II, and III only 
D)  II, III, and IV only 
E)  I, II, III, IV, and V 
A)  I and IV only 
B)  II and III only 
C)  I, II, and III only 
D)  II, III, and IV only 
E)  I, II, III, IV, and V

Question 15

At which phase(s)is it preferable to obtain chromosomes to prepare a karyotype?

Accepted Answer

A)  early prophase 
B)  late telophase 
C)  anaphase 
D)  late anaphase or early telophase 
E)  late prophase or metaphase 
A)  early prophase 
B)  late telophase 
C)  anaphase 
D)  late anaphase or early telophase 
E)  late prophase or metaphase

Question 16

Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?

Accepted Answer

A)  There are four major functional classes of genes in Drosophila. 
B)  Drosophila genes cluster into four distinct groups of linked genes. 
C)  The overall number of genes in Drosophila is a multiple of four. 
D)  The entire Drosophila genome has approximately 400 map units. 
E)  Drosophila genes have, on average, four different alleles. 
A)  There are four major functional classes of genes in Drosophila. 
B)  Drosophila genes cluster into four distinct groups of linked genes. 
C)  The overall number of genes in Drosophila is a multiple of four. 
D)  The entire Drosophila genome has approximately 400 map units. 
E)  Drosophila genes have, on average, four different alleles.

Question 17

What is the source of the extra chromosome 21 in an individual with Down syndrome?

Accepted Answer

A)  nondisjunction in the mother only 
B)  nondisjunction in the father only 
C)  duplication of the chromosome 
D)  nondisjunction or translocation in either parent 
E)  It is impossible to detect with current technology. 
A)  nondisjunction in the mother only 
B)  nondisjunction in the father only 
C)  duplication of the chromosome 
D)  nondisjunction or translocation in either parent 
E)  It is impossible to detect with current technology.

Question 18

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this alteration called?

Accepted Answer

A)  deletion 
B)  transversion 
C)  inversion 
D)  translocation 
E)  duplication 
A)  deletion 
B)  transversion 
C)  inversion 
D)  translocation 
E)  duplication

Question 19

Use the following information to answer the questions below.
A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine as follows:
A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type):
  
-In which progeny phenotypes has there been recombination between genes A and B?

Accepted Answer

A)  1, 2, 5, and 6 
B)  1, 3, 6, and 7 
C)  2, 4, 5, and 8 
D)  2, 3, 5, and 7 
E)  in all 8 of them 
A)  1, 2, 5, and 6 
B)  1, 3, 6, and 7 
C)  2, 4, 5, and 8 
D)  2, 3, 5, and 7 
E)  in all 8 of them

Question 20

A gene is considered to be non-Mendelian in its inheritance pattern if it seems to "violate" Mendel's laws. Which of the following would be considered Mendelian?

Accepted Answer

A)  a gene whose expression varies depending on the gender of the transmitting parent 
B)  a gene derived solely from maternal inheritance 
C)  a gene transmitted via the cytoplasm or cytoplasmic structures 
D)  a gene transmitted to males from the maternal line and from fathers to daughters 
E)  a gene transmitted by a virus to egg-producing cells 
A)  a gene whose expression varies depending on the gender of the transmitting parent 
B)  a gene derived solely from maternal inheritance 
C)  a gene transmitted via the cytoplasm or cytoplasmic structures 
D)  a gene transmitted to males from the maternal line and from fathers to daughters 
E)  a gene transmitted by a virus to egg-producing cells

Exam 15: The Chromosomal Basis of Inheritance

SRY is best described in which of the following ways?

Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons?

In 1956 Tijo and Levan first successfully counted human chromosomes. What is the reason it took so many years to do so?

An inversion in a human chromosome often results in no demonstrable phenotypic effect in the individual. What else may occur?

When Thomas Hunt Morgan crossed his red-eyed F₁ generation flies to each other, the F₂ generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?

Women (and all female mammals)have one active X chromosome per cell instead of two. What causes this?

Which of the following is the meaning of the chromosome theory of inheritance as expressed in the early 20th century?

In humans, clear gender differentiation occurs, not at fertilization, but after the second month of gestation. What is the first event of this differentiation?

At which phase(s)is it preferable to obtain chromosomes to prepare a karyotype?

Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?

What is the source of the extra chromosome 21 in an individual with Down syndrome?

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. What is this alteration called?

A gene is considered to be non-Mendelian in its inheritance pattern if it seems to "violate" Mendel's laws. Which of the following would be considered Mendelian?

Introduction: Themes in the Study of Life

The Chemical Context of Life

Water and Life

Carbon and the Molecular Diversity of Life

The Structure and Function of Large Biological Molecules

A Tour of the Cell

Membrane Structure and Function

An Introduction to Metabolism

Cellular Respiration and Fermentation

Photosynthesis

Cell Communication

The Cell Cycle

Meiosis and Sexual Life Cycles

Mendel and the Gene Idea

The Molecular Basis of Inheritance

From Gene to Protein

Regulation of Gene Expression

Viruses

Biotechnology

Genomes and Their Evolution

Descent with Modification: A Darwinian View of Life

The Evolution of Populations

The Origin of Species

The History of Life on Earth

Phylogeny and the Tree of Life

Bacteria and Archaea

Protists

Plant Diversity I: How Plants Colonized Land

Plant Diversity II: The Evolution of Seed Plants

Fungi

An Overview of Animal Diversity

An Introduction to Invertebrates

The Origin and Evolution of Vertebrates

Plant Structure, Growth, and Development

Resource Acquisition and Transport in Vascular Plants

Soil and Plant Nutrition

Angiosperm Reproduction and Biotechnology

Plant Responses to Internal and External Signals

Basic Principles of Animal Form and Function

Animal Nutrition

Circulation and Gas Exchange

The Immune System

Osmoregulation and Excretion

Hormones and the Endocrine System

Animal Reproduction

Animal Development

Neurons, Synapses, and Signaling

Nervous Systems

Sensory and Motor Mechanisms

Animal Behavior

An Introduction to Ecology and the Biosphere

Population Ecology

Community Ecology

Ecosystems and Restoration Ecology

Conservation Biology and Global Change

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