This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) 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
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.
2. 5 Bromo uracil can pair with _____________
a) Uracil
b) Thymine
c) Guanine
d) Cytosine
View Answer
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
Explanation: Deamination of guanine will give Xanthine, which also base pairs with Cytosine. Thus the base pairing is not changed.
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
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
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.
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
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
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.
8. In Ames test, the bacterial culture are grown in _________
a) Natural media
b) Blood agar
c) Enriched media
d) Minimal media
View Answer
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
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.
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
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.
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