Deck 6: Chromosome Mutations: Variation in Number and Arrangement

Question 1

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

Answer 1

rDNA

Question 2

What explanation is generally given for lethality of monosomic individuals?

Answer 2

Monosomy may unmask recessive lethals that are tolerated in heterozygotes carrying the wild -type allele.

Question 3

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

Answer 3

In 1970, Ohno proposed that gene duplication provides a way in which new genes arise. By duplicating a gene, the duplicated copy or the original gene is able to mutate without necessarily having an adverse influence on the
phenotype.

Question 4

Name the polyploid condition that is formed from the addition of one or more extra
sets of chromosomes identical to the normal haploid complement of the same species.

Question 5

Describe the maternal age effect associated with Down syndrome.

Question 6

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

Question 7

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

Question 8

The condition known as cri -du -chat syndrome in humans has a genetic constitution designated as _.
A) triploidy

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

Question 9

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 10

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

Question 11

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

Question 12

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.

Question 13

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 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 chromosome 21's) 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) None of the surviving offspring would be expected to have Down syndrome.
B) All the children would be expected to have Down syndrome.
C) One -half of the surviving offspring would be expected to have Down syndrome.
D) One -third of the surviving offspring would be expected to have Down syndrome.
E) Two -thirds of the surviving offspring would be expected to have Down syndrome.

Question 14

What is meant by the terms acentric and dicentric?

Question 15

Recently, a gene located on chromosome 3 in humans, FHIT, has been shown to be associated with _.

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

Question 16

Describe Bar mutations in Drosophila melanogaster.

Question 17

Given that a human normally contains 46 chromosomes, give the chromosome number for each of the following conditions:
Turner syndrome (female, no Barr bodies) Klinefelter syndrome (male, one Barr body) triploid
Down syndrome (trisomic) trisomy 13

Question 18

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

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

Question 19

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

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) multiple breakpoints fairly evenly dispersed along the X chromosome
C) single translocations in the X chromosome
D) various lengths of trinucleotide repeats
E) multiple inversions in the X chromosome

Question 21

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

Question 22

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 23

An individual with Patau syndrome would be called a triploid.

Question 24

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

Question 25

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

Question 26

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

Question 27

A deletion may set up a genetic circumstance where a recessive gene is expressed in an otherwise diploid organism.

Question 28

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

Question 29

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 30

Nondisjunction is viewed as a major cause of aneuploidy.

Question 31

The term aneuploidy is synonymous with the term segmental deletion.

Question 32

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

Question 33

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

Question 34

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

Question 35

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

Question 36

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

Question 37

A pericentric inversion includes the centromere.

Question 38

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

Question 39

rDNA in eukaryotes is typically redundant.

Question 40

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

Question 41

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.

Question 42

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

Question 43

Inversions and translocations are without evolutionary significance.

Question 44

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

Question 45

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

Question 46

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

Question 47

Translocations may be pericentric or paracentric.