Deck 15: The Dynamic Genome: Transposable Elements

Question 1

A corn plant is homozygous for a mutant allele that results in no pigment in the seed (i.e.,white).The mutant is caused by Ds insertion that often exits late in seed development,when there is an active Ac element in the genome.If there is NO active Ac element,the seeds of this plant will be:

A)no pigment (i.e. ,white).
B)pigmented all over.
C)white with small spots of pigment.
D)white with large spots of pigment.
E)weakly pigmented.

Answer 1

A

Question 2

In D.melanogaster,when M cytotype (lab stock)females are crossed to P cytotype (wild)males,the resulting F₁ progeny are:

A)normal.
B)defective.
C)normal:defective in a 1:1 ratio.
D)normal:defective in a 1:2:1 ratio.
E)normal:defective in a 3:1 ratio.

Answer 2

B

Question 3

Eukaryotic retrotransposons such as Ty1 and Copia are flanked by:

A)direct repeats (DRs).
B)inverted repeats (IRs).
C)long terminal repeats (LTRs).
D)long inverted repeats (LIRs).
E)None of the answer options are correct.

Answer 3

C

Question 4

Transposable elements that transpose via an RNA intermediate is known as:

A)class 1 elements.
B)class 2 elements.
C)class 3 elements.
D)alpha elements.
E)D elements.

Question 5

LINEs differ from retrotransposons in that LINEs do not:

A)encode transposase.
B)encode reverse transcriptase.
C)contain LTRs.
D)transpose in a replicative manner.
E)contain the transposase gene.

Question 6

An autonomous element:

A)requires no other elements for its mobility.
B)requires one additional element(s)for its mobility.
C)is only found in corn (maize).
D)is found only in plants.
E)None of the answer options are correct.

Question 7

What percentage of the human genome is derived from transposable elements?

A)less than 5%
B)25%
C)50%
D)75%
E)nearly 100%

Question 8

Bacterial transposon structure can be thought of as:

A)IS sequences flanked by inverted drug-resistance genes.
B)drug-resistance gene(s)flanked by IS elements.
C)drug-resistance gene(s)flanked by a pair of mu ( $\mu$ )phage.
D)a mu ( $\mu$ )phage flanked by two IS elements.
E)resistance gene(s)flanked by inverted resistance transfer factors (RTFs).

Question 9

A nonautonomous element:

A)requires no other elements for its mobility.
B)requires additional element(s)for its mobility.
C)is only found in corn (maize).
D)is found only in plants.
E)None of the answers are correct.

Question 10

Which of the following scientists discovered the Ac-Ds transposable elements in maize?

A)Marcus Rhoades
B)Rollins Emerson
C)Barbara McClintock
D)George Beadle
E)All of these scientists made the discovery.

Question 11

IS-induced mutations are different from missense mutations in that they are:

A)nonrevertible.
B)less severe.
C)more severe.
D)nonpolar.
E)not reverted by mutagens.

Question 12

The first eukaryotic transposable elements to be characterized at the molecular level were identified within the genes of which organism?

A)corn
B)yeast
C)E.coli
D)mouse
E)human

Question 13

Retrotransposons move via an intermediate that is:

A)a double-stranded lollipop.
B)a retrovirus.
C)double-stranded RNA.
D)single-stranded DNA.
E)single-stranded RNA.

Question 14

Hybridization of single-stranded wild-type DNA with DNA from mutations caused by IS elements characteristically shows (through electron microscopy):

A)chi structures.
B)unpaired tails.
C)a single-stranded loop representing IS DNA.
D)a single-stranded loop representing wild-type DNA.
E)theta structures.

Question 15

Transposable elements that are comprised of DNA transposons are known as:

A)class 1 elements.
B)class 2 elements.
C)class 3 elements.
D)alpha elements.
E)D elements.

Question 16

Retroviruses replicate using:

A)DNA polymerase.
B)RNA polymerase.
C)restriction endonuclease.
D)reverse transcriptase.
E)topoisomerase.

Question 17

Which of the following statements is/are TRUE about the P elements of Drosophila?

A)P elements are examples of eukaryotic DNA transposons.
B)P elements are mobilized when females with these elements are crossed to males that lack them.
C)P elements are silenced in M cytotype.
D)P elements are examples of eukaryotic DNA transposons that are mobilized when females with these elements are crossed to males that lack them.
E)P elements are examples of eukaryotic DNA transposons that are silenced in M cytotype.

Question 18

Which of the following features do bacterial and corn transposons not have in common?

A)Both may cause unstable mutations.
B)Both may carry drug resistance genes in natural populations.
C)Both may have inverted repeats.
D)Both may move to new loci.
E)Both may cause rearrangements.

Question 19

A corn plant is homozygous for a mutant allele that results in no pigment in the seed (i.e.,white).The mutant is caused by Ds insertion that often exits late in seed development,when there is an active Ac element in the genome.The seeds of this plant will be:

A)no pigment (i.e. ,white).
B)pigmented all over.
C)white with small spots of pigment.
D)white with large spots of pigment.
E)weakly pigmented.

Question 20

In D.melanogaster,when P cytotype (lab stock)females are crossed to M cytotype (wild)males,the resulting F₁ progeny are:

A)normal.
B)defective.
C)normal:defective in a 1:1 ratio.
D)normal:defective in a 1:2:1 ratio.
E)normal:defective in a 3:1 ratio.

Question 21

A maize plant is homozygous for an allele C^m,caused by the insertion of a Ds element into the coding region of a gene (C)that encodes an enzyme necessary for the synthesis of anthocyanin in maize kernels.
a)If this plant also contains an Ac element in its genome,what will be the phenotype of its kernels? Justify your answers.
b)If this plant does not contain an Ac element,what will be the kernel phenotype? Justify your answers.
c)If the plant does not contain an Ac element,but it does contain an autonomous element for another family of transposon,what will be the kernel phenotype? Justify your answers.

Question 22

Transposable elements can cause corn kernels to be spotted if they jump in or out of the color genes during the development of the kernel.However,the size of the spots can vary greatly.In words and diagrams,describe the difference between the two kernels shown below at the molecular and developmental levels.

Question 23

The movement of transposable elements can cause either forward mutations or reversions.
a)Define "forward mutations" and "reversions," and describe the transposition events that cause these two types of phenotypic changes.
b)Why did Barbara McClintock focus on reversions rather than forward mutations when she first studied the inheritance of transposable elements in maize?

Question 24

Which of the following statements is/are TRUE about the miniature inverted repeat transposable elements (MITEs)?

A)MITEs are examples of retrotransposons.
B)MITEs are examples of DNA transposons.
C)MITEs can attain very high copy numbers in humans.
D)MITEs contain transposase gene.
E)None of the answer options are correct.

Question 25

Compare and contrast autonomous and nonautonomous transposable elements.

Question 26

Compare and contrast IS elements,simple transposons,and composite transposons.Use diagrams to help in the comparison.

Question 27

Approximately 45 percent of the human genome is derived from transposable elements,such as LINEs and SINEs.
a)What are LINEs and SINEs?
b)How do LINEs differ from SINEs?
c)How is survival possible with this high a percentage of transposable elements in the human genome?

Question 28

The grasses (such as barley,rice,sorghum,and corn)vary widely in the size of their genomes,yet they are descended from a common ancestor.What accounts for the variation in DNA content (i.e.,the total amount of DNA)?

A)large-scale duplication of genes
B)large-scale loss of genes
C)accumulation of LTR retrotransposons
D)loss of LTR retrotransposons
E)None of the answer options are correct.

Question 29

Match the following transposable elements with the species where it is found.
i.humans (A)Dt element
ii.Drosophila (B)Ty1 element
iii.yeast (C)L1 element
iv.maize (D)P element

Question 30

a)What is the C-value paradox?
b)What is the explanation for the C-value paradox?