This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “DNA Mutation – 1”.
1. All mutations result in the production of a mutant.
Explanation: Any change in genetic constitution of the organism is termed as mutation, but only when the phenotypic expression is changed it is called a mutant.
2. Which of the following is not a point mutation?
Explanation: Point mutation concerns a single base. Thus substitution, which includes transversion, and insertion or deletion, falls within point mutation. On the other hand, translocation involves a stretch of bases so it is not a point mutation.
3. ‘Delicious apples’ can’t be propagated through_____________
d) Tissue culture
Explanation: Delicious apple was produced first as a somatic mutation within a branch and was since propagated vegetatively. As somatic mutations don’t affect germ cells, it can’t be propagated through seeds.
4. Which of the following harmful mutations will have the most severe effect in the progeny?
a) Mutation in a muscle tissue
b) Mutation in a gamete
c) Mutation in sperm mother cells
d) Mutation in mammary gland tissue
Explanation: Option a and d are somatic tissue, their mutation will not be propagated. A single gamete will only have a slight chance to fertilize and lead to mutation, but sperm mother mutation will produce many lethal gametes that will increase the probability.
5. The number of times a particular mutation occurs in a population of cells or individuals is known as __________
a) Mutation rate
b) Mutation frequency
c) Mutation count
d) Mutation efficiency
Explanation: While mutation frequency is the number of times a particular mutation occurs in a population, mutation rate is the probability of a particular type of mutation per unit time.
6. Total number of transition and transversion that can take place in genome is___________
a) 2 and 6
b) 6 and 4
c) 4 and 6
d) 4 and 8
Explanation: Transition is the replacement of a purine by another purine or a pyrimidine by another pyrimidine. Transversion is the replacement of a purine by a pyrimidine, or a pyrimidine by a purine. So there are 4 possible transition A—G and C— T, and 8 possible transversions A—C, A—T, G—C, G—T.
7. Sickle cell anemia is a result of _______________
a) Non sense mutation
b) Mis-sense mutation
c) Sense mutation
d) Frame shift mutation
Explanation: In this disease, a GAG is converted to a GUG, i.e a glutamic acid is converted to a valine. This is example of a mis-sense mutation where a change of base codes for a different amino acid from the original.
8. A frame shift mutation will have minimum effect when it leads to ______________
a) Insertion of 2 bases
b) Deletion of 1 base
c) Insertion of 3 bases
d) Deletion of 2 bases
Explanation: Frame shift mutations lead to lease effect when they lead to an insertion or deletion of 3 bases, as due to our codon being triplet this doesn’t shift the reading frame. However, if the codon thus lost or added is a very important one in the gene, there could be serious consequences.
9. Wooble base recognition of the tRNAs in translation ignores which of the mutation?
a) Frame shift
Explanation: Silent mutation is the one where two codons code for the same gene. Thus, conversion of one codon to another doesn’t effectively change the protein at all.
10. Which of the following is a neutral mutation?
a) Replacement of a Glu by Val
b) Replacement of AAA by UAA
c) Replacement of Lys by Arg
d) Replacement of Thr by Tyr
Explanation: Lys and Arg are both basic amino acid of similar size, thus the mutation of one with another doesn’t have much effect on the final protein structure or function. On the other hand, option b is a nonsense mutation, and a and d are missense mutation.
11. Which of the following is a result of a sense mutation?
a) Sickle cell anemia
c) Mutation in beta globin leading to abnormal clotting and bleeding
d) Down’s syndrome
Explanation: In Thalassemia the alpha globin is 141 amino acids long as the UAA codon is changed to CAA, i.e a stop codon is changed to a glutamic acid. While sickle cell anemia is due to a mis sense mutation and c is due to a nonsense mutation and d due to trisomy.
12. Which of the following can act as an intragenic suppressor mutation to a Frame shift mutation?
b) Missense mutation
c) Another frame shift mutation
d) Non sense mutation
Explanation: If overall the two frame shift mutations lead to a change of 3 or its multiple in the genetic code, the codons will again be in the same frame. This is an internal compensation, so intragenic suppression.
13. Which sequences among these will have a preference for frame shift?
Explanation: Repetitive sequences have a greater chance of frame shift mutation due to polymerase error. The polymerase tends to slide through these same sequences as even the base pairing is not much affected if it does so.
14. The normal form for A and C, and G and T are _____________
a) Imino and Keto
b) Imino and Enol
c) Amino and Enol
d) Amino and Keto
Explanation: The normal form of A and C is amino and that of G and T base is Keto. Shift to imino and enol form is due to tautomeric shift, it is a rare phenomenon.
15. In an experiment your germ cell was having a base at its unusual tautomeric state while replication. What could be the maximum percentage of germ cells carrying this mutation?
Explanation: It has been experimentally seen that a mutation can effect at max 50% of the progeny cells. This is due to the fact that there are two DNA strands and only one of them is carrying the mutation. So, only progenies receiving copies of that mutant strand will be mutant i.e. 50%.
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