Test Bank For Genetic Analysis 2nd Edition by Sanders – Test Bank

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Test Bank For Genetic Analysis 2nd Edition by Sanders – Test Bank

 

Sample  Questions

 

Genetics: An Integrated Approach (Sanders)

Chapter 3   Cell Division and Chromosome Heredity

3.1   Multiple-Choice Questions

1)    Mitosis is a process of cell division that results in __________.

  1. A) two unique daughter cells
  2. B) four unique daughter cells
  3. C) two identical daughter cells
  4. D) three identical daughter cells
  5. E) four identical daughter cells

Answer:  C

Section:  3.1

Skill:  Knowledge/Comprehension

2)    During which stage or phase of the cell cycle does the cell actively transcribe and translate at the highest rate all the protein products necessary for normal cellular structure and function?

  1. A) M phase
  2. B) G1
  3. C) G2
  4. D) S
  5. E) metaphase

Answer:  B

Section:  3.1

Skill:  Knowledge/Comprehension

3)    During which stage or phase of the cell cycle does the cell replicate its chromosomes?

  1. A) M phase
  2. B) G1
  3. C) G2
  4. D) S
  5. E) G0

Answer:  D

Section:  3.1

Skill:  Knowledge/Comprehension

4)    After which stage or phase of the cell cycle does cytokinesis occur?

  1. A) M phase
  2. B) G1
  3. C) G2
  4. D) S
  5. E) G0

 

Answer:  A

Section:  3.1

Skill:  Knowledge/Comprehension

5)    Certain kinds of cells (e.g., some cells in the eyes and bones) mature and differentiate into a state in which they have a specialized function but do not divide or progress through the cell cycle. These cells are “stuck” in which stage?

  1. A) M phase
  2. B) G1
  3. C) G2
  4. D) S
  5. E) G0

Answer:  E

Section:  3.1

Skill:  Knowledge/Comprehension

6)    During mitotic cell division, if chromosomal material is improperly divided between the two daughter cells, one cell could receive three copies of a chromosome, and the other cell could receive only one. This is likely due to a defect in which process?

  1. A) cytokinesis
  2. B) karyokinesis
  3. C) crossing over
  4. D) synapsis
  5. E) homologous recombination

Answer:  B

Section:  3.1

Skill:  Application/Analysis

7)    Scientists isolate two different cells from the same organism at different points in the cell cycle. Cell A has 1.5 times the DNA content of cell B. Which of the following is true?

  1. A) cell A is in G1 phase; cell B is in G2 phase
  2. B) cell B is in G1 phase; cell A is in G1 phase
  3. C) cell A is in S phase; cell B is in G1 phase
  4. D) cell B is in S phase; cell A is in G1 phase
  5. E) cell A is in S phase; cell B is in G2 phase

Answer:  C

Section:  3.1

Skill:  Application/Analysis

8)    During which cell cycle phase(s) are chromosomes composed of two DNA molecules?

  1. A) G2
  2. B) G1
  3. C) anaphase
  4. D) Answers (A) and (B) are correct.
  5. E) Answers (A), (B), and (C) are correct.

 

Answer:  A

Section:  3.1

Skill:  Application/Analysis

9)    You discover a new species of snail, Biologica terificia, and find that its haploid number is 4 (n = 4). The somatic cells of Biologica terificia are diploid. How many chromosomes are in a somatic cell of the snail in G1 phase?

  1. A) 4
  2. B) 8
  3. C) 16
  4. D) too many to count

Answer:  B

Section:  3.1

Skill:  Application/Analysis

10)  How many DNA molecules are in a somatic cell of the snail in G2 phase?

  1. A) 4
  2. B) 8
  3. C) 16
  4. D) too many to count

Answer:  C

Section:  3.1

Skill:  Application/Analysis

11)  The accompanying figure represents a chromosome at metaphase of mitosis. How many DNA molecules are present in this chromosome?

  1. A) one
  2. B) two
  3. C) four
  4. D) more than four
  5. E) impossible to determine

Answer:  B

Section:  3.1

Skill:  Application/Analysis

12)  Which organelle migrates during M phase to form the two opposite poles of the dividing cell and acts as the source of the spindle fiber microtubules?

  1. A) centromere
  2. B) kinetochore
  3. C) centrosome
  4. D) chiasmata
  5. E) chromosome

Answer:  C

Section:  3.1

Skill:  Knowledge/Comprehension

13)  Which structure is responsible for chromosome movement during cell division?

  1. A) synaptonemal complex
  2. B) kinetochore microtubules
  3. C) metaphase plate
  4. D) nuclear envelope
  5. E) cell membrane

Answer:  B

Section:  3.1

Skill:  Knowledge/Comprehension

14)  The separation of sister chromatids during anaphase I of mitosis is known as chromosome __________.

  1. A) cytokinesis
  2. B) karyokinesis
  3. C) crossing over
  4. D) synapsis
  5. E) disjunction

Answer:  E

Section:  3.1

Skill:  Knowledge/Comprehension

15)  A dihybrid has the genotype AaBb. After a normal mitotic division into two daughters cells, one daughter cell will have the genotype _____________ and the other will have the genotype ______________.

  1. A) Aa; Bb
  2. B) AaBb; AaBb
  3. C) AB; ab
  4. D) Ab; aB
  5. E) AABB; aabb

Answer:  B

Section:  3.1

Skill:  Application/Analysis

 

16)  How do protein kinases generally activate their target proteins?

  1. A) The process of phosphorylation causes the target proteins to change conformation.
  2. B) The kinases bind to target proteins directly, forming a complex that activates the proteins and lets them change conformation.
  3. C) Kinase concentrations vary during the cell cycle, so that proteins are activated only when kinase levels are high.
  4. D) Kinases bind to target proteins and inactivate them, so kinase levels must drop for target protein activation.
  5. E) The process of dephosphorylation causes the target proteins to change conformation.

Answer:  A

Section:  3.1

Skill:  Knowledge/Comprehension

17)  Tumor suppressors are genes that __________.

  1. A) promote advancement of the cell cycle
  2. B) phosphorylate proteins involved in the cell cycle
  3. C) block progression of the cell cycle
  4. D) prevent apoptosis in normal cells
  5. E) activate proto-oncogenes

Answer:  C

Section:  3.1

Skill:  Knowledge/Comprehension

18)  Vinblastine is a commonly used chemotherapy drug that acts by interfering with the assembly of microtubules. How does it likely target cancer cells?

  1. A) by suppressing cyclins
  2. B) by inhibiting protein kinases
  3. C) by inhibiting DNA synthesis
  4. D) by denaturing myosin and preventing the cleavage furrow from forming
  5. E) by disrupting mitotic spindle formation

Answer:  E

Section:  3.1

Skill:  Application/Analysis

19)  If you mutate the gene encoding a Cdk such that Cdk protein product cannot bind to cyclin, what effect would you expect to see?

  1. A) Cdk will be unaffected.
  2. B) The cell cycle will be up-regulated, and the cells will proliferate.
  3. C) Cdk will be inactive, so the target proteins will not be phosphorylated.
  4. D) Cdk will be constitutively active, so the cell cycle will be unchecked.
  5. E) Cdk will phosphorylate its target proteins regardless of the cell cycle.

Answer:  C

Section:  3.1

Skill:  Synthesis/Evaluation

 

20)  Mutations that inhibit Rb gene expression will have what effect on cell proliferation?

  1. A) Cells will proliferate less, even if excess growth factors are present.
  2. B) Cells will proliferate less because growth factors are absent.
  3. C) Cells will proliferate more because growth factors are produced in excess.
  4. D) Cells will proliferate more, regardless of growth factor concentration.
  5. E) There will be no effect on cell proliferation; only apoptosis occurs.

Answer:  D

Section:  3.1

Skill:  Application/Analysis

21)  During meiosis I, when does homologous chromosome pairing and recombination occur?

  1. A) prophase I
  2. B) pro-metaphase I
  3. C) metaphase I
  4. D) anaphase I
  5. E) telophase I

Answer:  A

Section:  3.2

Skill:  Knowledge/Comprehension

22)  The binding of nonsister chromatids by a synaptonemal complex draws the homologs into close contact so that what process can occur?

  1. A) cytokinesis
  2. B) karyokinesis
  3. C) independent assortment
  4. D) synapsis
  5. E) disjunction

Answer:  D

Section:  3.2

Skill:  Knowledge/Comprehension

23)  Contact points between nonsister chromatids that mark the locations of DNA-strand exchange are called __________.

  1. A) synaptonemal complexes
  2. B) metaphase plates
  3. C) chiasmata
  4. D) kinetochores
  5. E) centrosomes

Answer:  C

Section:  3.2

Skill:  Knowledge/Comprehension

24)  Genes A and B are on different chromosomes. A dihybrid with the genotype AaBb undergoes meiosis. Which of the following depicts a possible genotype in a gamete?

  1. A) Aa
  2. B) Bb
  3. C) AB
  4. D) A
  5. E) B
  6. F) AaBb

Answer:  C

Section:  3.2

Skill:  Application/Analysis

25)  WT yeast (TRP+) can synthesize the amino acid tryptophan and can grow on media plates lacking tryptophan. In contrast, mutant alleles (trp) block tryptophan synthesis and result in an inability of mutant strains to grow on media lacking tryptophan. A diploid yeast was made through the cross MATa ADE+ × MATα ade. Meiosis was induced in the diploid strain to produce an ascus with four haploid spores, which were separated and grown on plates lacking tryptophan. How many spores are expected to grow into colonies on the plate?

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 4

Answer:  C

Section:  3.2

Skill:  Application/Analysis

26)  A dihybrid has the genotype AaBb. The diagram depicts the chromosome composition of different cells from the animal. Which of the cells could represent a mature gamete?

  1. A) Cell G
  2. B) Cell H
  3. C) Cell K
  4. D) Cell M
  5. E) Cell P

Answer:  A

Section:  3.2

Skill:  Application/Analysis

 

27)  Which of the following represents the contents of a cell in G2 phase (before cell division begins)?

  1. A) Cell G
  2. B) Cell H
  3. C) Cell K
  4. D) Cell M
  5. E) Cell P

Answer:  D

Section:  3.2

Skill:  Application/Analysis

28)  Which of the following cells could be created from a mitotic division but would not be created during a normal meiosis?

  1. A) Cell G
  2. B) Cell H
  3. C) Cell K
  4. D) Cell M
  5. E) Cell P

Answer:  C

Section:  3.2

Skill:  Application/Analysis

 

29)  What insight did Nettie Stevens’s studies of the beetle Tenebrio molitor provide about the chromosome theory of inheritance?

  1. A) Genes are located on chromosomes.
  2. B) The number of autosomal chromosomes varied between gametes.
  3. C) Crossing over occurs between homologous chromosomes.
  4. D) Sex is determined by the presence of an X or Y chromosome in the male gamete.
  5. E) Chromosomes assort independently into the haploid gametes.

Answer:  D

Section:  3.3

Skill:  Knowledge/Comprehension

30)  Morgan’s analysis of a white-eyed male Drosophila mutation helped explain __________.

  1. A) autosomal dominance
  2. B) random mutation
  3. C) crossing over
  4. D) independent assortment
  5. E) X-linked inheritance

Answer:  E

Section:  3.3

Skill:  Knowledge/Comprehension

31)  Bridges showed that sex determination in Drosophila meant that __________.

  1. A) females were XX or XXX, and males were XY or XXY
  2. B) females were XX, and males were XY
  3. C) females were XX, and males were XY or XO
  4. D) females were XX or XXX, and males were XY or XO
  5. E) females were XX or XO, and males were XY or XXY

Answer:  D

Section:  3.4

Skill:  Knowledge/Comprehension

32)  A pure-breeding female fruit fly with a yellow body is crossed to a pure-breeding male fruit fly with a gray body. All female offspring from the cross have gray bodies and all males have yellow bodies. Body color is likely a(n)__________trait, and the gray allele is ________.

  1. A) Autosomal; dominant
  2. B) Autosomal; recessive
  3. C) X-linked; dominant
  4. D) X-linked; recessive

Answer:  C

Section:  3.5

Skill:  Application/Analysis

33)  If a trait is X-linked recessive, who would express the trait?

  1. A) females homozygous for the dominant allele and males hemizygous for the recessive allele
  2. B) heterozygous females and males hemizygous for the dominant allele
  3. C) females homozygous for the recessive allele and males hemizygous for the recessive allele

 

  1. D) females homozygous for the recessive allele and males hemizygous for the dominant allele
  2. E) the same proportions of females and males

Answer:  C

Section:  3.5

Skill:  Application/Analysis

34)  If a trait is X-linked dominant, who would express the trait?

  1. A) females homozygous for the dominant allele and males hemizygous for the recessive allele
  2. B) heterozygous females and males hemizygous for the dominant allele
  3. C) females homozygous for the recessive allele and males hemizygous for the recessive allele
  4. D) females homozygous for the recessive allele and males hemizygous for the dominant allele
  5. E) significantly more females than males

Answer:  B

Section:  3.5

Skill:  Application/Analysis

35)  What dosage compensation mechanism is employed by female placental mammals?

  1. A) synteny
  2. B) Y-inactivation
  3. C) X-inactivation
  4. D) X nondisjunction
  5. E) X chromosome crossing over

Answer:  C

Section:  3.6

Skill:  Knowledge/Comprehension

36)  Red-green color blindness is an X-linked recessive disorder. A woman with normal vision whose father was colorblind has children with a man with normal color vision. What is the probability that their first child will be colorblind?

  1. A) 1/4
  2. B) 1/2
  3. C) 3/4
  4. D) 0
  5. E) 1

Answer:  A

Section:  3.5

Skill:  Application/Analysis

3.2   Short-Answer Questions

1)    How many chromosomes are found in a human somatic cell nucleus?

Answer:  46

Section:  3.1

Skill:  Knowledge/Comprehension

 

2)    How many homologous pairs of chromosomes are found in a human somatic cell nucleus?

Answer:  23

Section:  3.1

Skill:  Knowledge/Comprehension

3)    How many total chromatids are found in a human somatic cell nucleus during G2 phase?

Answer:  92

Section:  3.1

Skill:  Application/Analysis

4)    What process is used to make mature germ-line cells, or gametes?

Answer:  meiosis

Section:  3.1

Skill:  Knowledge/Comprehension

5)    What is the short segment of the cell cycle during which genetic material is partitioned equally to two daughter cells?

Answer:  the M phase

Section:  3.1

Skill:  Knowledge/Comprehension

6)    If a cell begins to divide rapidly (as often seen in wound repair), what would you expect to happen to the G1 phase?

Answer:  It would shorten.

Section:  3.1

Skill:  Application/Analysis

7)    A cell in G1 phase has the option of entering which two phases?

Answer:  S phase or G0

Section:  3.1

Skill:  Knowledge/Comprehension

8)    The five substages of M phase are designed to accomplish two main goals: equal partitioning between the two cells of chromosomal material and of cytoplasmic contents. What are these two processes called?

Answer:  karyokinesis and cytokinesis

Section:  3.1

Skill:  Knowledge/Comprehension

9)    Microtubules are polar, having a plus-end and a minus-end. Which end is anchored at the centrosome?

Answer:  the minus end

Section:  3.1

Skill:  Knowledge/Comprehension

10)  Why are chromosomes more easily visible under the microscope during metaphase as compared to G2 phase?

Answer:  They have condensed 10,000-fold.

Section:  3.1

Skill:  Application/Analysis

11)  Protein kinases help phosphorylate target proteins, but they are present in relatively constant concentrations throughout the cell cycle. Which proteins, which vary during the cell cycle, form a complex with the kinases to activate them only at specific times?

Answer:  cyclins

Section:  3.1

Skill:  Knowledge/Comprehension

12)  When cyclin D1 is expressed in normal levels, it stimulates the cell cycle. If overexpressed, it can promote cancer by allowing cells to overproliferate. The normal cyclin D1 gene, which has the potential to cause cancer if mutated and/or overexpressed, is known as what?

Answer:  proto-oncogene

Section:  3.1

Skill:  Knowledge/Comprehension

13)  Single-celled eukaryotes can survive and reproduce in both haploid and diploid forms. Yeast spend most of their life cycle and actively reproduce in which form?

Answer:  haploid

Section:  3.2

Skill:  Knowledge/Comprehension

14)  What separates in meiosis I to reduce the diploid number (2n) of chromosomes to the haploid number (n)?

Answer:  homologous chromosomes

Section:  3.2

Skill:  Knowledge/Comprehension

15)  At the end of meiosis II, what is produced?

Answer:  four haploid gametes

Section:  3.2

Skill:  Knowledge/Comprehension

16)  The gametes of the two sexes are often dramatically different in size and morphology. If both gametes have a haploid nuclei, then what do female gametes contain more of?

Answer:  cytoplasm and organelles

Section:  3.2

Skill:  Application/Analysis

 

17)  The number of occurrences of which event correlates closely with the number of recombination nodules along each homologous chromosome arm?

Answer:  crossover event

Section:  3.2

Skill:  Knowledge/Comprehension

18)  Which protein assures that sister chromatids of each chromosome remain firmly joined and can resist the pull of the kinetochore microtubules?

Answer:  cohesin

Section:  3.2

Skill:  Knowledge/Comprehension

19)  Females have two copies of the X chromosome, so they can be homozygous or heterozygous for any genes found on the X chromosome. Males have only one copy of the X chromosome. What term is used to describe this inheritance state?

Answer:  hemizygous

Section:  3.3

Skill:  Knowledge/Comprehension

20)  According to Bridges’s proposal, exceptional phenotypes and unusual karyotypes were the result of rare mistakes in meiosis caused by the failure of X chromosomes to separate properly in either the first or second meiotic division in females. What term is used in referring to this phenomenon?

Answer:  nondisjunction

Section:  3.3

Skill:  Knowledge/Comprehension

21)  What is the mammalian transcription factor that elicits a cascade of gene transcription and developmental events that ultimately produce male internal and external structures?

Answer:  SRY

Section:  3.4

Skill:  Knowledge/Comprehension

22)  Which term describes any mechanism that compensates for differences in the number of copies of genes due to the different chromosome constitutions of males and females?

Answer:  dosage compensation

Section:  3.6

Skill:  Knowledge/Comprehension

3.3   Fill-in-the-Blank Questions

1)    Of the trillions of cells in the human body, most are ________, the cells that form organs and tissues.

Answer:  somatic cells

Section:  3.1

Skill:  Knowledge/Comprehension

2)    The ________ varies among species (each species has its characteristic number of pairs) and is identified nonspecifically as 2n.

Answer:  diploid number

Section:  3.1

Skill:  Knowledge/Comprehension

3)    The ________ number, or n, is the number of chromosomes contained in the nuclei of gametes, the nonsomatic cells.

Answer:  haploid

Section:  3.1

Skill:  Knowledge/Comprehension

4)    In meiosis, interphase is followed by two successive rounds of cell division, meiosis I and II. Meiosis results in four haploid daughter cells because there is no ________ between these two meiotic cell divisions.

Answer:  DNA replication

Section:  3.2

Skill:  Knowledge/Comprehension

5)    Synapsis initiates formation of a protein bridge called the synaptonemal complex, a tri-layer protein structure that maintains synapsis by tightly binding ________ of homologous chromosomes to one another.

Answer:  nonsister chromatids

Section:  3.2

Skill:  Knowledge/Comprehension

6)    An individual is heterozygous for a gene at a specific locus. Sister chromatids will have _______ (the same form/different form) of alleles at that locus after S phase.

Answer:  the same form

Section:  3.1

Skill:  Application/Analysis

3.4   Essay Questions

1)    What is the difference between cytokinesis and karyokinesis? Which process needs to be more precise for accurate cell division?

Answer:  Karyokinesis is the equal partitioning of the chromosomal material in the nucleus of the parental cell between the nuclei of the two daughter cells. This process requires first that each of the chromosomes in the nucleus be fully and accurately duplicated and then that the duplicate copies of each chromosome be separated so that one copy goes to the nucleus of one daughter cell and the second copy goes to the other daughter nucleus. Karyokinesis is followed by cytokinesis, the partitioning of the cytoplasmic contents of the parental cell into the daughter cells.

Cytokinesis does not demand the same degree of equivalency required in karyokinesis. The cytoplasm of the parental cell contains an abundance of the proteins and organelles that the daughter cells require in order to function, so the division of this material need not be equal.

Section:  3.1

Skill:  Synthesis/Evaluation

2)    What are three important differences between mitosis and meiosis I?

Answer:

In meiosis I, but not in mitosis, the following three processes occur:

  1. Homologous chromosome pairing
  2. Crossing over between homologous chromosomes
  3. Segregation (separation) of the homologous chromosomes, which reduces chromosomes to the haploid number

Section:  3.2

Skill:  Synthesis/Evaluation

3)    Describe how microtubules and cohesion work together to align the chromosomes along the metaphase plate during the process of sister chromatid cohesion.

Answer:  Kinetochore microtubules are attached to the kinetochore at each centromere of sister chromatids. Because they are tethered to kinetochore microtubules from opposite centrosomes, the sister chromatids experience opposing forces that are critical to the positioning of chromosomes along an imaginary midline at the equator of the cell. This imaginary line is called the metaphase plate. The tension created by the pull of kinetochore microtubules is balanced by a companion process known as sister chromatid cohesion. Sister chromatid cohesion is produced by the protein cohesin that localizes between the sister chromatids and holds them together to resist the pull of kinetochore microtubules. As microtubules move chromosomes toward the midline of the cell, cohesin helps keep the sister chromatids together to ensure proper chromosome positioning and to prevent their premature separation.

Section:  3.2

Skill:  Synthesis/Evaluation

4)    Which meiotic division(s) reduce(s) chromosome number (i.e., meiosis I, meiosis II, or both)? Explain your answer.

Answer:  Meiosis I reduces chromosome number when homologs separate. After meioisis I, each cell contains a haploid number of chromosomes. Meiosis II reduces DNA content, but does not reduce chromosome number.

Section:  3.2

Skill:  Synthesis/Evaluation

5)    Describe how Mendel’s two laws are illustrated by the movement of chromosomes in meiosis.

Answer:  Mendel’s Law of Segregation is illustrated in meiosis I when homologs separate. Alternate alleles of a gene found on homologs segregate from each other and end up in separate gametes. Mendel’s Law of Independent Assortment is illustrated by the behavior of two pairs of homologs during metaphase I. The alignment of one homologous pair is independent of the alignment of other pairs.

Section:  3.2

Skill:  Application/Analysis

6)    How do cyclin-dependent kinases help regulate the cell cycle?

Answer:  As cells move through the cell cycle, readiness to progress from one stage to the next is regularly assessed. Numerous cell cycle checkpoints are monitored for cell readiness by protein interactions. A common mechanism for this monitoring is carried out by protein complexes that join a protein kinase with a second protein known as a cyclin protein. Protein kinases catalyze protein phosphorylation—the addition of a phosphate group transferred from a nucleotide triphosphate such as ATP or GTP to a target protein. Phosphorylation changes the conformation of target proteins and can either activate or inactivate the target protein. Protein kinases are usually present continuously in cells at relatively steady concentrations. Cyclin proteins, however, are so named because their concentrations are cyclic and linked to the cell cycle stage. Cyclin protein production is stimulated by growth factor proteins that are produced by other cells. The protein kinase components of these complexes are activated only when they associate with a cyclin; thus, the protein kinases are called cyclin-dependent kinases, or Cdks. In their activated state, cyclin–Cdk complexes phosphorylate numerous target proteins and regulate cell cycle progression at various checkpoints.

Section:  3.1

Skill:  Synthesis/Evaluation

 

Genetics: An Integrated Approach (Sanders)

Chapter 5   Genetic Linkage and Mapping in Eukaryotes

5.1   Multiple-Choice Questions

1)    Syntenic genes can assort independently when __________.

  1. A) they are very close together on a chromosome
  2. B) they are located on different chromosomes
  3. C) crossing over occurs rarely between the genes
  4. D) they are far apart on a chromosome and crossing over occurs frequently between the genes
  5. E) they are far apart on a chromosome and crossing over occurs very rarely between the genes

Answer:  D

Section:  5.1

Skill:  Knowledge/Comprehension

2)    The alleles of linked genes tend to __________.

  1. A) segregate together during gamete production
  2. B) assort independently
  3. C) be mutated more often than unlinked genes
  4. D) experience a higher rate of crossing over
  5. E) assort independently and show a higher rate of crossing over

Answer:  A

Section:  5.1

Skill:  Knowledge/Comprehension

3)    Genetic linkage leads to the production of a significantly greater than expected number of gametes containing chromosomes with __________.

  1. A) allele combinations that are different from parental combinations
  2. B) parental combinations of alleles
  3. C) mutant alleles
  4. D) dominant alleles
  5. E) recessive alleles

Answer:  B

Section:  5.1

Skill:  Knowledge/Comprehension

4)    The syntenic genes A and Z are linked. A cross between two parents, AAZZ and aazz, produces F1 progeny with the AaZz genotype. What are the possible arrangements of alleles on the F1 progeny’s chromosomes?

  1. A) AZ/az
  2. B) Az/aZ
  3. C) Aa/Zz
  4. D) AZ/Az or az/aZ
  5. E) A/Z or a/z

Answer:  A

Section:  5.1

Skill:  Application/Analysis

5)    In a dihybrid cross exhibiting complete genetic linkage, what would you expect?

  1. A) one parental allele combination occurring more frequently than another
  2. B) two equally frequent gametes containing only parental allele combinations
  3. C) only recombinant gametes
  4. D) one parental allele combination occurring more frequently than another and no recombinant gametes
  5. E) two equally frequent gametes containing only parental allele combinations and no recombinant gametes

Answer:  E

Section:  5.1

Skill:  Application/Analysis

6)    In a two-point test-cross analysis, a dihybrid F1 fly is crossed to a __________.

  1. A) pure-breeding mate with a dominant phenotype (AABB)
  2. B) pure-breeding mate with a recessive phenotype (aabb)
  3. C) heterozygote mate (AaBb)
  4. D) mate that is dominant for one gene and recessive for the other (AAbb or aaBB)
  5. E) second dihybrid F1 fly (sibling cross)

Answer:  B

Section:  5.1

Skill:  Knowledge/Comprehension

7)    In fruit flies, red eyes (pr+_) are dominant to purple eyes (prpr) and normal wings (vg+_) are dominant to vestigial wings (vgvg). The genes are located on the same chromosome. A purebreeding red-eyed fly with vestigial wings was crossed with a pure-breeding purple-eyed fly with normal wings. All of the F1 progeny had a WT phenotype. Which of the following represents the arrangement of alleles on the F1’s chromosome?

  1. A) prvg/pr+vg+
  2. B) pr+vg/prvg+
  3. C) prpr+/vgvg+
  4. D) prvg/prvg
  5. E) pr+vg+/pr+vg+

Answer:  B

Section:  5.1

Skill:  Application/Analysis

8)    In fruit flies, red eyes (pr+_) are dominant to purple eyes (prpr) and normal wings (vg+_) are dominant to vestigial wings (vgvg). The genes are located on the same chromosome. A purebreeding red-eyed fly with vestigial wings was crossed with a pure-breeding purple-eyed fly with normal wings. All of the F1 progeny had a WT phenotype. The recombination frequency between the two genes is 10%. If an F1 individual was test crossed, what percentage of the progeny would you expect to have the WT phenotype?

 

  1. A) 5%
  2. B) 10%
  3. C) 50%
  4. D) 90%
  5. E) 95%

Answer:  A

Section:  5.1

Skill:  Application/Analysis

9)    If you are given a recombination frequency of 34% between genes X and Y and 27% between X and Z, can you predict the order of the three genes?

  1. A) Yes; the order is X-Z-Y.
  2. B) Yes; the order is X-Y-Z.
  3. C) Yes; the order is Z-X-Y.
  4. D) No; based on this data alone, the order could be Z-Y-X or X-Y-Z.
  5. E) No; based on this data alone, the order could be X-Z-Y or Z-X-Y.

Answer:  E

Section:  5.2

Skill:  Application/Analysis

10)  What type of test would you use to determine whether observed data constitute evidence of genetic linkage or are simply a case of chance variation from expected values?

  1. A) test cross
  2. B) two-point test cross
  3. C) three-point test cross
  4. D) chi-square analysis
  5. E) recombination frequency (r) calculation

Answer:  D

Section:  5.2

Skill:  Knowledge/Comprehension

11)  You perform a test cross of the dihybrid AaBb and score the phenotypes of 1000 progeny. Assuming independent assortment, how many of the progeny do you expect to display the dominant phenotype for both the A and B genes?

  1. A) 100
  2. B) 200
  3. C) 250
  4. D) 500
  5. E) 750

Answer:  C

Section:  5.2

Skill:  Application/Analysis

12)  Incomplete genetic linkage of three genes in a trihybrid produces eight genetically different gamete genotypes. How many different gamete genotypes are produced in a four-gene cross with incomplete genetic linkage?

  1. A) 4
  2. B) 8
  3. C) 16
  4. D) 20
  5. E) 24

Answer:  C

Section:  5.3

Skill:  Application/Analysis

13)  Assuming three genes are linked, how many recombinant genotypes would you expect and at what frequency?

  1. A) two recombinant genotypes, more frequent than expected by independent assortment
  2. B) four recombinant genotypes, more frequent than expected by independent assortment
  3. C) six recombinant genotypes, more frequent than expected by independent assortment
  4. D) four recombinant genotypes, less frequent than expected by independent assortment
  5. E) six recombinant genotypes, less frequent than expected by independent assortment

Answer:  E

Section:  5.3

Skill:  Knowledge/Comprehension

14)  For a given cross, the expected number of double recombinants is 20 and the observed number of double recombinants is 15. What is the coefficient of coincidence (c)?

  1. A) 25
  2. B) 33
  3. C) 20
  4. D) 75
  5. E) 15

Answer:  D

Section:  5.3

Skill:  Application/Analysis

15)  For a given cross, the expected number of double recombinants is 20 and the observed number of double recombinants is 15. What is the interference calculation (I)?

  1. A) 25
  2. B) 33
  3. C) 20
  4. D) 75
  5. E) 15

Answer:  A

Section:  5.3

Skill:  Application/Analysis

16)  Genes A and B are located 10cM from each other on a chromosome. Gene C is located 25cM from gene A and 15cM from gene B. Assuming that I = 0, what is the probability that the trihybrid ABC/abc will produce an ABC gamete?

  1. A) 5%
  2. B) 25%
  3. C) 25%
  4. D) 5%
  5. E) .75%

Answer:  B

Section:  5.3

Skill:  Application/Analysis

17)  Genes A and B are located 10cM from each other on a chromosome. Gene C is located 25cM from gene A and 15cM from gene B. What is the probability that the trihybrid ABC/abc will produce any kind of recombinant gamete?

  1. A) 5%
  2. B) 25%
  3. C) 5%
  4. D) 5%
  5. E) 75%

Answer:  C

Section:   5.3

Skill:  Application/Analysis

18)  Where does crossing over occur?

  1. A) at the centromeres
  2. B) at the telomeres
  3. C) at nodules that occur randomly at “hotspots” along the synaptonemal complex
  4. D) at nodules that occur in specific, evenly spaced locations along a chromosome
  5. E) at both the centromeres and telomeres

Answer:  C

Section:  5.4

Skill:  Knowledge/Comprehension

19)  When does recombination occur?

  1. A) before DNA replication
  2. B) at the two-strand stage, when each member of a homologous chromosome pair is composed of two sister chromatids, and before DNA replication
  3. C) at the four-strand stage, when each member of a homologous chromosome pair is composed of two sister chromatids, and before DNA replication
  4. D) at the two-strand stage, when the sister chromatids have been separated, and after DNA replication
  5. E) at the four-strand stage, when each member of a homologous chromosome pair is composed of two sister chromatids, and after DNA replication

Answer:  E

Section:  5.4

Skill:  Knowledge/Comprehension

20)  Which type of crossover event produces no recombinant chromosomes?

  1. A) single-strand crossover
  2. B) two-strand double crossover
  3. C) three-strand double crossover
  4. D) four-strand double crossover
  5. E) None of the above; all crossover events produce recombinant chromosomes.

Answer:  B

Section:  5.4

Skill:  Knowledge/Comprehension

21)  Which type of crossover event produces two parental and two recombinant chromosomes in gametes?

  1. A) single-strand crossover
  2. B) two-strand double crossover
  3. C) three-strand double crossover
  4. D) four-strand double crossover
  5. E) None of the above; all crossover events produce only recombinant chromosomes.

Answer:  C

Section:  5.4

Skill:  Knowledge/Comprehension

22)  Which type of crossover event produces all four recombinant chromosomes?

  1. A) single-strand crossover
  2. B) two-strand double crossover
  3. C) three-strand double crossover
  4. D) four-strand double crossover
  5. E) None of the above; all crossover events produce a combination of parental and recombinant chromosomes.

Answer:  D

Section:  5.4

Skill:  Knowledge/Comprehension

23)  For a given haplotype, the frequencies of alleles for gene Y are Y = 0.65 and Y’ = 0.35, and the frequencies at gene Z are Z = 0.25 and Z’ = 0.75. What is the predicted frequency of the Y¢Z¢ haplotype?

  1. A) 16
  2. B) 26
  3. C) 74
  4. D) 84
  5. E) 1

Answer:  B

Section:  5.6

Skill:  Application/Analysis

24)  Intragenic recombination can be detected __________.

  1. A) based on recombination between homologs carrying different mutant alleles
  2. B) by the recovery of 100% double-mutant chromosomes
  3. C) by the recovery of both wild-type and double-mutant chromosomes
  4. D) based on recombination between homologs with different mutant alleles and recovery of 100% double-mutant chromosomes
  5. E) based on recombination between homologs with different mutant alleles and recovery of both wild-type and double-mutant chromosomes

Answer:  E

Section:  5.4

Skill:  Application/Analysis

25)  After analysis of 100 pedigrees, the Zmax from the analysis of linkage between a disease gene D and the DNA marker P was found to be 3.5 at θ = 0.25. Which of the following is the best interpretation of these results?

  1. A) No conclusion can be made regarding linkage of D and P.
  2. B) The evidence supports linkage of D and P at 25 cM.
  3. C) The evidence supports linkage of D and P at 2.5 cM.
  4. D) The evidence supports linkage of D and P at 0.25 cM.
  5. E) The evidence indicates that D and P are not linked.

Answer:  B

Section:  5.5

Skill:  Application/Analysis

26)  The Zmax from the analysis of a disease gene N and the DNA marker H was 2.5 at θ = 0.1. Which of the following is the best interpretation of this result?

  1. A) N and H are not linked.
  2. B) N and H are separated by 10 cM.
  3. C) N and H are separated by more than 10 cM.
  4. D) N and H are separated by less than 10 cM.
  5. E) No conclusion can be made regarding the linkage of N and H.

Answer:  E

Section:  5.5

Skill:  Application/Analysis

5.2   Short-Answer Questions

1)    What is observed when syntenic genes are close enough to one another that they are unable to assort independently?

Answer:  genetic linkage

Section:  5.1

Skill:  Knowledge/Comprehension

2)    What is the term for chromosomes that do not reshuffle the alleles of linked genes?

Answer:  parental chromosomes

Section:  5.1

Skill:  Knowledge/Comprehension

 

3)    Recombination analysis allows for the mapping of genes because the frequency of crossing over is proportional to what distance?

Answer:  distance between genes

Section:  5.1

Skill:  Knowledge/Comprehension

4)    What organism exhibits complete genetic linkage, meaning there is no recombination between homologous chromosomes?

Answer:  male Drosophila or Diptera

Section:  5.1

Skill:  Knowledge/Comprehension

5)    Incomplete genetic linkage is far more common than complete linkage. What is the term for gametes produced when recombination shuffles the alleles of linked genes?

Answer:   nonparental or recombinant gametes

Section:  5.1

Skill:  Knowledge/Comprehension

6)    Two genes, A and X, exhibit incomplete linkage. The frequency of each parental gamete (AX and ax) is 45%. What is the approximate frequency of the Ax gamete?

Answer:  5%

Section:  5.1

Skill:  Application/Analysis

7)    There are three genes located in the gene order A-B-C on a chromosome. Would you expect the recombination frequency to be higher between A and B or A and C?

Answer:  higher between A and C (they are farther apart)

Section:  5.1

Skill:  Application/Analysis

8)    Morgan realized that Bateson and Punnett had detected genetic linkage but they couldn’t explain their results because they performed the wrong cross. What type of cross did Morgan use for the analysis of genetic linkage of autosomal genes in Drosophila?

Answer:  two-point test-cross analysis

Section:  5.1

Skill:  Knowledge/Comprehension

9)    In a two-point test-cross analysis, what are the “two points” being tested?

Answer:  the two genes

Section:  5.1

Skill:  Knowledge/Comprehension

10)  What unit of physical distance between genes on a chromosome provides a convenient way to relate the recombination frequencies for linked genes with their positions and order along a chromosome?

Answer:  map unit (m.u.) or centimorgan (cM)

Section:  5.2

Skill:  Knowledge/Comprehension

11)  What type of test would you use to determine the relative order of more than two genes?

Answer:  three-point test-cross

Section:  5.3

Skill:  Knowledge/Comprehension

12)  In most tests of genetic linkage, the number of double crossovers is less than the number expected due to what effect, which limits the number of crossovers that can occur in a short length of chromosome?

Answer:  interference (I)

Section:  5.3

Skill:  Knowledge/Comprehension

13)  Refer to this map to answer the questions:

  1. a) What is the distance between gene E and gene F?
  2. b) Assuming I = 0, what is the probability of no crossovers between gene D and gene E?
  3. c) Assuming I = 0, what is the probability of no crossovers between gene E and gene F?
  4. d) Considering both gene pairs, what is the proportion of nonrecombinant gametes?
  5. e) What is the predicted frequency of each parental gamete (DEF/def )?
  6. f) What is the recombination frequency between gene D and gene E?
  7. g) What is the recombination frequency between gene E and gene F?
  8. h) What is the frequency of two single recombinant gametes between genes D and E?
  9. i) What is the frequency of two single recombinant gametes between genes E and F?
  10. j) What is the frequency of each of the double-recombinant gametes, DeF and dEf?
  11. k) Fill in the blanks below to prove that the sum of the frequencies of the eight predicted gamete genotypes is equal to 1.0:

_______ + _______ + _______ + _______ + _______ + _______ + _______ + _______ = 1

DEF            def             Def            dEF            DEf            deF            DeF           dEf

Answer:  a)  12 cM

  1. b) 92%
  2. c) 88%
  3. d) (0.92)(0.88) = 0.8096
  4. e) (0.5)(0.8096) = 0.4048
  5. f) 8%
  6. g) 12%
  7. h) (0.08)(0.88)(0.5) = 0.0352
  8. i) (0.12)(0.92)(0.5) = 0.0552
  9. j) (0.08)(0.12)(0.5) = 0.0048
  10. k) 4048 + 0.0048 + 0.0352 + 0.0352 + 0.0552 + 0.0552 + 0.0048 + 0.0048 = 1

Section:  5.3

Skill:  Synthesis/Evaluation

14)  When constructing a genetic map of Zea mays, Creighton and McClintock used genetic markers as well as structural differences in the homologous copies of chromosome 9 that can be seen under the microscope. What are these structural differences called?

Answer:  cytological markers

Section:  5.4

Skill:  Knowledge/Comprehension

15)  What is the highest possible frequency of recombination between linked genes that can be generated by any type of crossover event?

Answer:  50%

Section:  5.4

Skill:  Knowledge/Comprehension

16)  Recombination frequency between linked genes increases as the distance between genes gets larger or gets smaller?

Answer:  larger

Section:  5.4

Skill:  Knowledge/Comprehension

17)  Recombination frequency differs between males and females. Which sex has a higher rate of recombination, heterogametic (males) or homogametic (females)?

Answer:  homogametic (females)

Section:  5.4

Skill:  Knowledge/Comprehension

18)  If there is a maximum Lod score of 4.2 at θ = 0.31, what can you say about the linkage and the distance between two genes?

Answer:  linked and 31 cM apart

Section:  5.5

Skill:  Application/Analysis

19)  If too little time has passed for crossing over to randomize haplotypes or if natural selection favors certain haplotypes, what would you expect to see?

Answer:  linkage disequilibrium

Section:  5.6

Skill:  Knowledge/Comprehension

20)  Ascospores in yeast are not arranged in a particular order. Thus, the four haploid ascospores contained within a yeast ascus are known as what?

Answer:  unordered tetrad

Section:  5.7

Skill:  Knowledge/Comprehension

 

5.3   Fill-in-the-Blank Questions

1)    A chromosome with a different combination of alleles than parental that is created by crossing over between homologous chromosomes is termed ________.

Answer:  recombinant chromosome

Section:  5.1

Skill:  Knowledge/Comprehension

2)    Alleles of linked genes usually segregate together during meiosis. When they don’t, it is because ________ has occurred between them.

Answer:  crossing over

Section:  5.1

Skill:  Knowledge/Comprehension

3)    Genetic linkage can be spotted by comparing the observed frequencies of ________ with the frequencies expected (assuming independent assortment).

Answer:  gamete genotypes/progeny phenotypes

Section:  5.1

Skill:  Knowledge/Comprehension

4)    5% recombination is equal to ________ map unit(s) (m.u.) or centimorgan(s) (cM) of distance between linked genes.

Answer:  5

Section:  5.2

Skill:  Application/Analysis

5)    The specific array of alleles making up a set of linked genes on a single chromosome is called a ________.

Answer:  haplotype

Section:  5.6

Skill:  Knowledge/Comprehension

5.4   Essay Questions

1)    What is the relationship between linked genes and syntenic genes? Are syntenic genes always linked?Are linked genes always syntenic? Describe what is meant by each term.

Answer:  Linked genes are always inherited together with no independent assortment. Syntenic genes are genes found on the same chromosome. Linked genes are always found on the same chromosome, but they are unable to sort independently because there is no crossing over observed between these two genes. Syntenic genes can be unlinked, and their alleles will assort independently if they are far enough apart on the chromosome for crossing over to generate independent assortment of the alleles.

Section:  5.1

Skill:  Synthesis/Evaluation

 

2)    The mapping of the human genome in the mid-1980s was integral for identifying new human genetic markers because of the identification of what types of polymorphic DNA markers?

Answer:  SNPs and restriction fragments

Section:  5.5

Skill:  Knowledge/Comprehension

3)    Describe why allelic phase is a major obstacle in mapping human genes.

Answer:  Allelic phase is the arrangement of different alleles of linked genes on homologous parental chromosomes. Allelic phase is required for genetic linkage analysis because you need to know which alleles are unique to “parental” and “recombinant” gametes.

Section:  5.5

Skill:  Synthesis/Evaluation

4)    How is Newton Morton’s statistical method helpful for calculating the overall probability of genetic linkage when allelic phase is unknown?

Answer:  Morton’s method determines whether genetic linkage exists between genes for which allelic phase is unknown by comparing the likelihood of obtaining the genotypes and phenotypes observed in a pedigree if two genes are linked versus the likelihood of getting the same pedigree structure if the genes assort independently. This approach assesses the probability of genetic linkage between two genes at a time and compares the probability of genetic linkage to the probability of independent assortment of the genes.

Section:  5.5

Skill:  Synthesis/Evaluation

5)    What is the Lod score?

Answer:  The ratio of the two likelihoods described in answer 4 above gives the “odds” of genetic linkage, and the Logarithm of the odds ratio generates the Lod score, a statistical value representing the probability of genetic linkage between two genes. A Lod score is a statistic that can attain significance favoring genetic linkage if the probability of genetic linkage is sufficiently greater than the probability of independent assortment, or significance against genetic linkage if the probability of independent assortment is sufficiently greater than the linkage probability. Lod scores can be interpreted for individual families, or they can be added together for as many families as are analyzed.

Section:  5.5

Skill:  Knowledge/comprehension

6)    What would a Lod score of 3.2 tell you about genetic linkage? What information does the θ value tell you?

Answer:  Scores of greater than 3.0 provide evidence of genetic linkage. θ values that correspond to a significant Lod score indicate an approximate distance (in cM) between linked genes.

Section:  5.5

Skill:  Synthesis/Evaluation

7)    Describe the three types of tetrads that can be formed when a diploid yeast sporulates to form haploid gametes.

Answer:  Parental ditypes (PD) contain four haploid cells with the same alleles seen in the parental class.

Nonparental ditypes (NPD) contain four recombinant haploid cells because the two parental alleles have recombined to form a nonparental combination of alleles.

Tetratype tetrads (TT) contain four different kinds of haploid cells: two parental spores and two recombinant spores. When two genes are not linked, tetratypes arise when a crossover occurs between one of the two genes and its centromere.

Section:  5.7

Skill:  Application/Analysis

8)    What ratios of these three tetrads would you expect to see if two genes are linked? Why is each type of tetrad more or less common? What ratios would you expect to see if the two genes are unlinked? Why?

Answer:  If two genes are linked, you will see that PD > TT > NPD. PD tetrads are most common; they are produced when no crossover occurs between genes and when two-strand double crossover takes place. TT tetrads are less frequent than PD; they occur when single crossovers or three-strand double crossovers take place. NPD tetrads are least frequent; they form only when four-strand double crossover occurs.

If PD = NPD, then the two genes are unlinked. This ratio indicates that either the genes are located on different chromosomes or they are syntenic but very far apart.

Section:  5.7

Skill:  Synthesis/Evaluation

9)    The products of meiosis yield the following results:

PD = 1200                       TT = 750                     NPD = 50

What is the recombination frequency?

Answer:

RF  = [(NPD + 1/2TT)/total # tetrads] × 100

= [(50 + 1/2(750)/2000] × 100

= 21.25 m.u.

Section:  5.7

Skill:  Synthesis/Evaluation

10)  Crossing over occurs frequently during meiosis. Can crossing over occur during mitosis? Explain why mitotic crossing over may or may not be possible.

Answer:  Mitotic crossover is a rare event. Mitotic crossing over occurs only in diploid (somatic) cells; thus, to study mitotic crossing over in a haploid organism, diploid cells have to be created artificially. Mitotic crossing over most likely occurs when homologous chromosomal segments are accidentally paired in somatic cells since it requires that after DNA replication, but before homologous chromosomes randomly align along the metaphase plate, the homologous chromosomes come together and interact like chromosomes during prophase I in meiosis. Opportunities for this unusual kind of mitotic interaction are rare but variable by species. Although rare, mitotic crossing over is important in some organisms. Some fungi that do not have a sexual cycle use mitotic crossing over to introduce genetic variation. In humans, mitotic crossing over is thought to be important in allowing recessive cancer-causing mutations such as RB.

Section:  5.8

Skill:  Synthesis/Evaluation