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Genetics: A Conceptual Approach

Benjamin Pierce

Chapter 8

Chromosome Variation - all with Video Answers

Educators

Chapter Questions

02:56

Problem 1

List the three basic categories of chromosome mutations and define each one.

Sulav Pokhrel
Sulav Pokhrel
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01:37

Problem 2

Why do extra copies of genes sometimes cause drastic phenotypic effects?

Sulav Pokhrel
Sulav Pokhrel
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02:59

Problem 3

Draw a pair of chromosomes as they would appear during synapsis in prophase I of meiosis in an individual heterozygous for a chromosome duplication.

Sulav Pokhrel
Sulav Pokhrel
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02:24

Problem 4

What is haploinsufficiency?

Sulav Pokhrel
Sulav Pokhrel
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02:52

Problem 5

What is the difference between a paracentric and a pericentric inversion?

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Sulav Pokhrel
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01:28

Problem 6

How can inversions in which no genetic information is lost or gained cause phenotypic effects?

Sulav Pokhrel
Sulav Pokhrel
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02:12

Problem 7

Explain, with the aid of a drawing, how a dicentric bridge is produced when crossing over takes place in an individual heterozygous for a paracentric inversion.

Sulav Pokhrel
Sulav Pokhrel
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02:03

Problem 8

Explain why recombination is suppressed in individuals heterozygous for paracentric and pericentric inversions.

Sulav Pokhrel
Sulav Pokhrel
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01:36

Problem 9

How do translocations in which no genetic information is lost or gained produce phenotypic effects?

Sulav Pokhrel
Sulav Pokhrel
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06:19

Problem 10

Sketch the chromosome pairing and the different segregation patterns that can arise in an individual heterozygous for a reciprocal
translocation.

Dennis Howard
Dennis Howard
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04:24

Problem 11

What is a Robertsonian translocation?

Sulav Pokhrel
Sulav Pokhrel
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02:06

Problem 12

List four major types of aneuploidy.

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Sulav Pokhrel
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03:05

Problem 13

What is the difference between primary Down syndrome and familial Down syndrome? How does each type arise?

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03:24

Problem 14

What is uniparental disomy and how does it arise?

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02:00

Problem 15

What is genetic mosaicism and how does it arise?

Sulav Pokhrel
Sulav Pokhrel
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03:35

Problem 16

What is the difference between autopolyploidy and allopolyploidy? How does each arise?

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Sulav Pokhrel
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02:10

Problem 17

Explain why autopolyploids are usually sterile, whereas allopolyploids are often fertile.

Sulav Pokhrel
Sulav Pokhrel
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02:06

Problem 18

Examine the karyotypes shown in Figure 8.1 and Figure 8.2. Are the individuals from whom these karyotypes were made males or females?

Sulav Pokhrel
Sulav Pokhrel
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04:08

Problem 19

Which types of chromosome mutations
a. increase the amount of genetic material in a particular chromosome?
b. increase the amount of genetic material in all chromosomes?
c. decrease the amount of genetic material in a particular chromosome?
d. change the position of DNA sequences in a single chromosome without changing the amount of genetic material?
e. move DNA from one chromosome to a nonhomologous chromosome?

Sulav Pokhrel
Sulav Pokhrel
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02:47

Problem 20

A chromosome has the following segments, where \cdot represents the centromere: $$\underline{\mathrm{AB} \cdot \mathrm{CDEFG}}$$
What types of chromosome mutations are required to change this chromosome into each of the following chromosomes? (In some cases, more than one chromosome mutation may be required.)
(FIGURE CANNOT COPY)

Parvati Devi
Parvati Devi
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01:43

Problem 21

A chromosome initially has the following segments: $$\underline{\mathrm{AB} \cdot \mathrm{CDEFG}}$$ Draw the chromosome, identifying its segments, that would result from each of the following mutations.
a. Tandem duplication of DEF
b. Displaced duplication of DEF
c. Deletion of $\mathrm{FG}$
d. Paracentric inversion that includes DEFG
e. Pericentric inversion of BCDE

Parvati Devi
Parvati Devi
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01:36

Problem 22

The following diagram represents two nonhomologous chromosomes: $$\underline{\mathrm{AB} \cdot \mathrm{CDEFG}}$$ $$\underline{\mathrm{RS} \cdot \mathrm{TUVWX}}$$
What type of chromosome mutation would produce each of the following groups of chromosomes?
(FIGURE CANNOT COPY)

Parvati Devi
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03:32

Problem 23

The Notch mutation is a deletion on the X chromosome of Drosophila melanogaster. Female flies heterozygous for Notch have an indentation on the margins of their wings; Notch is lethal in the homozygous and hemizygous conditions. The Notch deletion covers the region of the X chromosome that contains the locus for white eyes, an X-linked recessive trait. Give the phenotypes and proportions of progeny produced in the following crosses.
a. A red-eyed Notch female is mated with a white-eyed male.
b. A white-eyed Notch female is mated with a red-eyed male.
c. A white-eyed Notch female is mated with a white-eyed male.

Sulav Pokhrel
Sulav Pokhrel
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01:56

Problem 24

The green-nose fly normally has six chromosomes: two metacentric and four acrocentric. A geneticist examines the chromosomes of an oddlooking green-nose fly and discovers that it has only five chromosomes; three of them are metacentric and two are acrocentric. Explain how this change in chromosome number might have taken place.

Sulav Pokhrel
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07:26

Problem 25

A wild-type chromosome has the following segments: $$\underline{\mathrm{RS} \cdot \mathrm{DEFGHI}}$$
Researchers have found individuals that are heterozygous for each of the following chromosome mutations. For each mutation, sketch how the wild-type and mutated chromosomes would pair in prophase I of meiosis, showing all chromosome strands.
(FIGURE CANNOT COPY)

Parvati Devi
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01:16

Problem 26

For the chromosomes shown in Figure $8.12,$ draw the chromatids that would result from a two-strand double crossover: one crossover between C and D and the other crossover between D and E.

Parvati Devi
Parvati Devi
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01:56

Problem 27

As discussed in this chapter, crossing over within a pericentric inversion produces chromosomes that have extra copies of some genes and no copies of other genes. The fertilization of gametes containing chromosomes with duplications or deletions often result in children with syndromes characterized by developmental delay, intellectual disability, abnormal development of organ systems, and early death. Maarit Jaarola and colleagues examined individual sperm cells of a male who was heterozygous for a pericentric inversion on chromosome 8 and determined that crossing over took place within the pericentric inversion in $26 \%$ of the meiotic divisions (M. Jaarola, R. H. Martin, and T. Ashley. $1998 .$ American Journal of Human Genetics $63: 218-224$ ). Assume that you are a genetic counselor and that a couple seeks counseling from you. Both the man and the woman are phenotypically normal, but the woman is heterozygous for a pericentric inversion on chromosome $8 .$ The man is karyotypically normal. What is the probability that this couple will produce a child with a debilitating syndrome as the result of crossing over within the pericentric inversion?

Sulav Pokhrel
Sulav Pokhrel
Numerade Educator
06:29

Problem 28

An individual heterozygous for a reciprocal translocation possesses the following chromosomes: (FIGURE CANNOT COPY)
a. Draw the pairing arrangement of these chromosomes in prophase I of meiosis.
b. Diagram the alternate, adjacent-1, and adjacent-2 segregation patterns in anaphase I of meiosis.
c. Give the products that result from alternate, adjacent-1, and adjacent-2 segregation.

Sana Riaz
Sana Riaz
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02:48

Problem 29

Red-green color blindness is a human X-linked recessive disorder. A young man with a $47,$ XXY karyotype (Klinefelter syndrome) is color blind. His $46,$ XY brother is also color blind. Both parents have normal color vision. Where did the nondisjunction that gave rise to the young man with Klinefelter syndrome take place? Assume that no crossing over took place in prophase I of meiosis.

Sulav Pokhrel
Sulav Pokhrel
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03:09

Problem 30

Junctional epidermolysis bullosa (JEB) is a severe skin disorder that results in blisters over the entire body. The disorder is caused by autosomal recessive mutations at any one of three loci that help to encode laminin $5,$ a major component in the dermal-epidermal basement membrane. Leena Pulkkinen and colleagues described a male newborn who was born with JEB and died at 2 months of age (L. Pulkkinen et al. 1997. American Journal of Human Genetics $61: 611-619$ ); the child had healthy, unrelated parents. Chromosome analysis revealed that the infant had 46 normal-appearing chromosomes. Analysis of DNA showed that his mother was heterozygous for a JEB-causing allele at the $L A M B 3$ locus, which is on chromosome $1 .$ The father had two normal alleles at this locus. DNA fingerprinting demonstrated that the male assumed to be the father had, in fact, conceived the child.
a. Assuming that no new mutations occurred in this family, explain the presence of an autosomal recessive disease in the child when the mother is heterozygous and the father is homozygous normal.
b. How might you go about proving your explanation? Assume that a number of genetic markers are available for each chromosome.

Sana Riaz
Sana Riaz
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02:08

Problem 31

Some people with Turner syndrome are $45, X / 46, X Y$ mosaics. Explain how this mosairism rould arise,

Sulav Pokhrel
Sulav Pokhrel
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03:11

Problem 32

Bill and Betty have had two children with Down syndrome. Bill's brother has Down syndrome and his sister has two children with Down syndrome. On the basis of these observations, indicate which of the following statements are most likely correct and which are most likely incorrect. Explain your reasoning.
a. Bill has 47 chromosomes.
b. Betty has 47 chromosomes.
c. Bill and Betty's children each have 47 chromosomes.
d. Bill's sister has 45 chromosomes.
e. Bill has 46 chromosomes.
f. Betty has 45 chromosomes.
g. Bill's brother has 45 chromosomes.

Sulav Pokhrel
Sulav Pokhrel
Numerade Educator
02:13

Problem 33

In mammals, sex-chromosome aneuploids are more common than autosomal aneuploids, but, in fishes, sex-chromosome aneuploids and autosomal aneuploids are found with equal frequency. Offer a possible explanation for these differences between mammals and fishes. (Hint:
Think about why sex-chromosome aneuploids are more common than autosomal aneuploids in mammals.)

Sulav Pokhrel
Sulav Pokhrel
Numerade Educator
02:23

Problem 34

A young couple is planning to have children. Knowing that there have been a substantial number of stillbirths, miscarriages, and fertility problems on the husband's side of the family, they see a genetic counselor. A chromosome analysis reveals that, whereas the woman has a normal karyotype, the man possesses only 45 chromosomes and is a carrier of a Robertsonian translocation between chromosomes 22 and
13.
a. List all the different types of gametes that might be produced man.
b. What types of zygotes will develop when each of gametes produced by the man fuses with a normal gamete produced by the woman?
c. If trisomies and monosomies entailing chromosomes 13 and 22 are lethal, approximately what proportion of the surviving offspring are expected to be carriers of the translocation?

Sulav Pokhrel
Sulav Pokhrel
Numerade Educator
05:32

Problem 35

Using breeding techniques, Andrei Dyban and V. S. Baranov (Cytogenetics of Mammalian Embryonic Development. Oxford: Oxford University Press, Clarendon Press; New York: Oxford University Press,
1987) created mice that were trisomic for each of the different mouse chromosomes. They found that only mice with trisomy 19 developed. Mice that were trisomic for all other chromosomes died in the course of development. For some of these trisomics, the researchers plotted the length of development (number of days after conception before the embryo died) as a function of the size of the mouse chromosome that was present in three copies (see the adjoining graph). Summarize their findings and provide a possible explanation for the results.

Sana Riaz
Sana Riaz
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