Cytogenetics Questions and Answers – DNA Mutation – 2

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This set of Cytogenetics test focuses on “DNA Mutation – 2”.

1. You are studying a mutational hot spot in the promoter region of a gene. Which type of mutation will you expect the most in this case?
a) Deamination
b) Depurination
c) Methylation
d) Frame shift
View Answer

Answer: a
Explanation: Mutational hot spots are regions which are rich in 5MC and these on deamination give a T base. Under normal condition deamination of C gives a U which is spontaneously excised out, but as T is a normal DNA base the mutation is fixed.
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2. 5 Bromo uracil can pair with _____________
a) Uracil
b) Thymine
c) Guanine
d) Cytosine
View Answer

Answer: c
Explanation: This is a base analogue that is a pyrimidine. Under normal conditions it behaves like T and base pairs with A; but under abnormal conditions, it behaves as C and Base pair with G. As a pyrimidine can’t base pair with another pyrimidine, G is the only available option.

3. Deamination of which of the bases which nitrous acid will not lead to any change in the base pairing?
a) A
b) G
c) C
d) T
View Answer

Answer: b
Explanation: Deamination of guanine will give Xanthine, which also base pairs with Cytosine. Thus the base pairing is not changed.
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4. Which of the following agents can lead to both addition and deletion mutation?
a) UV
b) 5 Bromo Uracil
c) Proflavin
d) Hydroxylation
View Answer

Answer: c
Explanation: Proflavin, like Ethidium bromide is an intercalating agent. This when inserted in DNA can lead to addition of a random base, and when lost can lead to deletion.

5. Which of the mutations can be detected Phenotypically?
a) Silent
b) Neutral
c) Reverse
d) Sense
View Answer

Answer: d
Explanation: All the other mutation lead to wild phenotype, so unless a genetic analysis is performed, they are indistinguishable. But in case of sense a stop codon is changed to a coding codon which has a serious phenotypic effect on the protein.
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6. Reverse and suppressor mutations both result in wild phenotype. Thus they are both indistinguishable by any test performed on phenotype.
a) True
b) False
View Answer

Answer: b
Explanation: Suppressor mutations are visible in the back cross as they are due to compensation and not a reversion to wild codon like reverse mutation. Thus, they can be distinguished by phenotypic study of back cross progeny.

7. Which of the following mutation will lead to AT->GC transition?
a) Nitrous acid acting on A
b) Nitrous acid on C
c) Hydroxylation of C
d) Methylation of G
View Answer

Answer: a
Explanation: All options other than oxidation of A by nitrous acid lead to GC->AT transition. Nitrous acid converts A to Hypoxanthine that in place of pairing with T pairs with C. Thus, it leads to AT->GC transition.
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8. In Ames test, the bacterial culture are grown in _________
a) Natural media
b) Blood agar
c) Enriched media
d) Minimal media
View Answer

Answer: d
Explanation: Only prototroph can grow in minimal media. In the Ames test, the mutagenicity of a substance is tested by its ability to convert an auxotroph into a prototroph. Thus to check for mutants, the media must be minimal so that only mutant colonies grow.

9. In an experiment to check mutagenicity of a substance, we feed the mutagen to a rat and then use the rat _______ extract within the media. This ensures_____________
a) Kidney; the mutagen can be at a higher concentration
b) Liver; the media has adequate iron from rat RBC
c) Liver; the mutagen is processed
d) Kidney; the mutagen is broken down
View Answer

Answer: c
Explanation: Rat is a mammal similar to human being. In us the food undergoes several processing steps than it would in case of a simple prokaryote like bacteria. Thus, using a rat liver extract ensures that the functional state of the substance is in the extract ensuring more efficiency. Liver processed all the toxins so its extract is used.
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10. Which of this mutagen can lead to both AT->GC and GC->AT transition?
a) Ethydium bromide
b) 5 Bromo uracil
c) MMS
d) NH2OH
View Answer

Answer: b
Explanation: 5 Bromo Uracil when incorporates in the DNA in a normal state and then undergoes transition to a rare state in the next replication cycle leads to an AT->GC mutation. While when it incorporates against a G in excited state and then undergoes replication when in the normal state it gives GC->AT transition.

Sanfoundry Global Education & Learning Series – Cytogenetics.

To practice all areas of Cytogenetics for tests, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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