Deck 8: Chromosome Mutations: Variation in Number and Arrangement

Question 1

Deletions are chromosomal aberrations in which some portion of a chromosome is missing. Describe a method using Drosophila deletions to determine the actual, physical location of a gene.

Answer 1

Cross homozygous mutant flies to homozygous wild-type flies that have been irradiated (or those with a series of known deletions-see below). Select mutant flies in the F₁. Those of the F₁ that display the mutant phenotype may have resulted from the wild-type allele being deleted by the X-ray treatment. Establish a stock of the exceptional mutant fly; then examine polytene chromosomes in larvae. The mutation in question may be contained in the compensation loop in the homolog of the deleted chromosome. If a series of known deletions is available (and these do exist in stock centers throughout the world), one can test (by the mating described above) the mutation against each deletion. Obviously, this would be a very time-consuming task unless one had some prior knowledge as to the general location of the mutant gene. This can be accomplished using balancer chromosomes and standard linkage determination. Once the mutant gene is "exposed" by a given deletion, a series of additional deletions can be used to "fine map" the region and determine a fairly accurate location for the gene.

Question 2

The condition known as cri-du-chat syndrome in humans has a genetic constitution designated as ________.

A) 45, X
B) heteroplasmy
C) 46, 5p-
D) triploidy
E) trisomy

Answer 2

C

Question 3

Name the polyploid condition that is formed from the addition of an extra set of chromosomes identical to the normal diploid complement of the same species.

Answer 3

autotetraploidy, assuming the normal chromosome complement is diploid

Question 4

The condition that exists when an organism gains or loses one or more chromosomes but not a complete haploid set is known as ________.

A) polyploidy
B) euploidy
C) aneuploidy
D) triploidy
E) trisomy

Question 5

What is meant by the terms acentric and dicentric?

Question 6

Recently, a gene located on chromosome 3 in humans, FHIT, has been shown to be associated with the significant human malady known as ________.

A) cancer
B) Huntington disease
C) "mad-cow" disease
D) Klinefelter syndrome
E) XYY/XY mosaicism

Question 7

Trisomics are observed in humans; monosomics are not. Why?

Question 8

Colchicine is an alkaloid derived from plants. What is its effect on chromosome behavior?

Question 9

Trisomy 21, or Down syndrome, occurs when there is a normal diploid chromosomal complement but one (extra) chromosome 21. While there is reduced fertility in both sexes, females have higher fertility than males. Van Dyke et al. (1995; Down Syndrome Research and Practice 3(2):65-69) summarize data involving children born of Down syndrome individuals. Given the fact that conceptuses with 48 chromosomes (four #21 chromosomes) are not likely to survive early development, what percentage of surviving offspring would be expected to have Down syndrome if both parents have Down syndrome?

A) One-third of the surviving offspring would be expected to have Down syndrome.
B) All the children would be expected to have Down syndrome.
C) None of the surviving offspring would be expected to have Down syndrome.
D) Two-thirds of the surviving offspring would be expected to have Down syndrome.
E) One-half of the surviving offspring would be expected to have Down syndrome.

Question 10

Describe the maternal age effect associated with Down syndrome.

Question 11

Inversion heterokaryotypes are often characterized as having reduced crossing over and reduced fertility. Assume that you were examining a strain of organisms you knew to be inversion heterokaryotypes and saw a relatively high number of double chromatid bridges extending between anaphase I nuclei. What would be a likely explanation for this observation? Explain with a labeled diagram.

Question 12

Describe Bar mutations in Drosophila melanogaster.

Question 13

In what way might gene duplication play a role in evolution?

Question 14

What explanation is generally given for lethality of monosomic individuals?

Question 15

Name two methods used in genetic prenatal diagnostic testing in humans.

Question 16

Provide an example of gene redundancy that occurs in both eukaryotes and prokaryotes.

Question 17

Trisomy 21, or Down syndrome, occurs when there is a normal diploid chromosomal complement but one (extra) chromosome 21. Although fertility is reduced in both sexes, females have higher fertility rates than males. Van Dyke et al. (1995; Down Syndrome Research and Practice 3(2): 65-69) summarize data involving children born of Down syndrome individuals. Assume that children are born to a female with Down syndrome and a normal 46-chromosome male. What proportion of the offspring would be expected to have Down syndrome?

A) One-third of the offspring would be expected to have Down syndrome.
B) Two-thirds of the offspring would be expected to have Down syndrome.
C) All the children would be expected to have Down syndrome.
D) None of the offspring would be expected to have Down syndrome.
E) One-half of the offspring would be expected to have Down syndrome.

Question 18

Although the most frequent forms of Down syndrome are caused by a random error, nondisjunction of chromosome 21, Down syndrome occasionally runs in families. The cause of this form of familial Down syndrome is ________.

A) an inversion involving chromosome 21
B) a chromosomal aberration involving chromosome 1
C) too many X chromosomes
D) a translocation between chromosome 21 and a member of the D chromosome group
E) a maternal age effect

Question 19

Clearly illustrate the pairing configuration of an inversion (paracentric) heterokaryotype.

Question 20

A genomic condition that may be responsible for some forms of fragile X syndrome, as well as Huntington disease, involves ________.

A) plasmids inserted into the FMR-1 gene
B) various lengths of trinucleotide repeats
C) multiple breakpoints fairly evenly dispersed along the X chromosome
D) multiple inversions in the X chromosome
E) single translocations in the X chromosome

Question 21

An expected meiotic pairing configuration in a triploid would be a trivalent.

Question 22

Assume that a species has a diploid chromosome number of 24. The term applied to an individual with 36 chromosomes would be triploid.

Question 23

Doubling the chromosomes of a sterile species hybrid with colchicine or cold shock is a method used to produce a fertile species hybrid (amphidiploid).

Question 24

Gene duplications provide an explanation for the origin of gene families.

Question 25

Assume that an organism has a haploid chromosome number of 7. There would be 14 chromosomes in a monoploid individual of that species.

Question 26

Inversions suppress crossing over by providing a chemical imbalance because of breakpoints within certain genes.

Question 27

Fragile X syndrome (or Martin-Bell syndrome) is the most common form of inherited mental retardation in humans. Is it more common in males or females? What is FMR1?

Question 28

Under what circumstance can an individual with Down syndrome have 46 chromosomes?

Question 29

An autotriploid may arise when three sperm cells are involved in fertilization of a single egg.

Question 30

Nondisjunction is viewed as a major cause of aneuploidy.

Question 31

The term aneuploidy is synonymous with the term segmental deletion.

Question 32

Assume that an organism has a diploid chromosome number of 14. There would be 28 chromosomes in a tetraploid.

Question 33

A paracentric inversion is one whose breakpoints do not flank the centromere.

Question 34

Assume that a species has a diploid chromosome number of 24. The term applied to an individual with 25 chromosomes would be triploid.

Question 35

In Drosophila melanogaster (2n = 8), a fly with seven chromosomes could be called a haplo-IV.

Question 36

Chorionic villus sampling (CVS) is sometimes preferred to amniocentesis because results can be provided earlier in the pregnancy.

Question 37

An individual with Patau syndrome would be called a triploid.

Question 38

A pericentric inversion includes the centromere.

Question 39

rDNA in eukaryotes is typically redundant.

Question 40

The chromosomal aberration that causes cri du chat syndrome can be referred to as a segmental deletion.

Question 41

Translocations may be pericentric or paracentric.

Question 42

Individuals with familial Down syndrome are trisomic and have 47 chromosomes.

Question 43

Familial Down syndrome is caused by a translocation involving chromosome 21.

Question 44

In general, inversion and translocation heterozygotes are as fertile as organisms whose chromosomes are in the standard arrangement.

Question 45

Inversions and translocations are without evolutionary significance.

Question 46

Familial Down syndrome can be caused by a translocation between chromosomes 1 and 14.

Question 47

A position effect occurs when a gene's expression is altered by virtue of a change in its position. One might expect position effects to occur with inversions and translocations.