NEET Biology Molecular Basis of Inheritance MCQs Set 29

Answer: (b) Inactive repressor + corepressor = active repressor

Explanation:
1. In a repressible operon the repressor is inactive alone.
2. It becomes active when a corepressor (end product) binds, and then the operon is switched off.
3. Hence option (b) is correct: Inactive repressor + corepressor = active repressor

Teacher's Note:
1. Repressible = switched off by the end product.
2. Inducible = switched on by the substrate.

Answer: (c) Lactose dehydrogenase

Explanation:
1. The lac operon makes beta-galactosidase, permease and transacetylase.
2. Lactose dehydrogenase is not made by it.
3. Hence option (c) is correct: Lactose dehydrogenase

Teacher's Note:
1. The lac operon has three enzymes only.
2. Learn z, y and a.

Answer: (c) Jacob and Monod (1961)

Explanation:
1. Jacob and Monod (1961) proposed the operon model with structural, promoter, operator and regulator genes.
2. Beadle and Tatum gave one gene - one enzyme.
3. Hence option (c) is correct: Jacob and Monod (1961)

Teacher's Note:
1. The lac operon was worked out in E. coli.

Answer: (b) Operator

Explanation:
1. The operator is a DNA sequence to which the repressor binds.
2. This blocks the RNA polymerase from reaching the promoter.
3. Hence option (b) is correct: Operator

Teacher's Note:
1. Repressor + operator = operon off.
2. The inducer removes the repressor.

Answer: (c) z, y, a

Explanation:
1. The structural genes of the lac operon are arranged as z, y, a.
2. They are transcribed together as one mRNA.
3. Hence option (c) is correct: z, y, a

Teacher's Note:
1. Z-Y-A is the order.
2. Remember it as the order of enzymes.

Answer: (a) An abrupt or discontinuous change which is inherited

Explanation:
1. A mutation is a sudden change in the genetic material that is inherited.
2. It is not just a change in the body that disappears.
3. Hence option (a) is correct: An abrupt or discontinuous change which is inherited

Teacher's Note:
1. Mutations are the raw material of evolution.
2. Only germ-line mutations are inherited.

Answer: (b) Translocation

Explanation:
1. Exchange of parts between non-homologous chromosomes is translocation.
2. Crossing over occurs between homologous chromosomes.
3. Hence option (b) is correct: Translocation

Teacher's Note:
1. Translocation can cause genetic disorders.
2. Inversion reverses a segment within one chromosome.

Answer: (a) n = 21, x = 7

Explanation:
1. Hexaploid wheat has 2n = 42, so n = 21.
2. The basic number x = 7 because 6x = 42.
3. Hence option (a) is correct: n = 21, x = 7

Teacher's Note:
1. Haploid number n is half of 2n, and the basic number x is 2n divided by the ploidy level.
2. In wheat x = 7.

Answer: (a) UV-rays

Explanation:
1. UV rays are non-ionizing radiation used to induce mutations.
2. Beta rays, X rays and gamma rays are ionizing.
3. Hence option (a) is correct: UV-rays

Teacher's Note:
1. UV is absorbed by purines and pyrimidines.
2. It causes thymine dimers.

Answer: (b) Transversion

Explanation:
1. A change of a purine to a pyrimidine or the reverse is a transversion.
2. A change of purine to purine is a transition.
3. Hence option (b) is correct: Transversion

Teacher's Note:
1. Transition = like for like.
2. Transversion = purine and pyrimidine swapped.

Answer: (b) Point mutation

Explanation:
1. Sickle-cell anaemia is caused by a single base change, GAG to GUG, in the beta chain gene.
2. So glutamic acid becomes valine.
3. Hence option (b) is correct: Point mutation

Teacher's Note:
1. A single base change is a point mutation.
2. Frame shift needs insertion or deletion.

Answer: (a) Deletion

Explanation:
1. Cri-du-chat syndrome is caused by deletion of the short arm of chromosome 5.
2. Babies have a cat-like cry.
3. Hence option (a) is correct: Deletion

Teacher's Note:
1. Deletion = loss of a segment.
2. Learn syndromes with the chromosome number.

Answer: (d) frame shift

Explanation:
1. Addition or deletion of one or two nucleotides shifts the reading frame.
2. This is called a frame-shift mutation.
3. Hence option (d) is correct: frame shift

Teacher's Note:
1. Frame shift changes all codons after the change.
2. Substitution does not shift the frame.

Answer: (d) inversion

Explanation:
1. The segment 'cde' has been reversed to 'edc'.
2. A reversed segment within a chromosome is an inversion.
3. Hence option (d) is correct: inversion

Teacher's Note:
1. Inversion = 180 degree turn of a segment.
2. No gene is lost or gained.

Answer: (d) monosomy

Explanation:
1. Loss of one chromosome from the diploid number (2n - 1) is monosomy.
2. 2n + 1 is trisomy.
3. Hence option (d) is correct: monosomy

Teacher's Note:
1. Aneuploidy changes one or a few chromosomes.
2. Euploidy changes whole sets.

Answer: (d) Northern blotting

Explanation:
1. DNA fingerprinting uses restriction digestion, gel electrophoresis, Southern blotting and hybridisation with a probe.
2. Northern blotting is for RNA.
3. Hence option (d) is correct: Northern blotting

Teacher's Note:
1. Southern = DNA, Northern = RNA, Western = protein.

Answer: (c) 'a' and 'd'

Explanation:
1. RFLP is analysed by digesting DNA with restriction enzymes and separating the fragments by electrophoresis.
2. Electroporation and methylation are not used.
3. Hence option (c) is correct: 'a' and 'd'

Teacher's Note:
1. RFLP = differences in fragment lengths.
2. They are seen as band patterns on a gel.

Answer: (c) western blotting

Explanation:
1. Transfer of proteins from a gel to a nitrocellulose membrane is western blotting.
2. Southern is for DNA and Northern for RNA.
3. Hence option (c) is correct: western blotting

Teacher's Note:
1. Antibodies are used to detect the protein on the membrane.

Answer: (a) Major peak; Minor peak

Explanation:
1. On density gradient centrifugation the bulk DNA forms a major peak and the satellite DNA forms a minor peak.
2. Satellite DNA has a different base composition.
3. Hence option (a) is correct: Major peak; Minor peak

Teacher's Note:
1. Satellite DNA is repetitive DNA.
2. It is the basis of VNTR and DNA fingerprinting.

Answer: (b) Digestion of DNA by DNA ligase enzyme

Explanation:
1. DNA is cut with restriction enzymes, not with DNA ligase.
2. Ligase joins DNA fragments.
3. Hence option (b) is correct: Digestion of DNA by DNA ligase enzyme

Teacher's Note:
1. Restriction enzyme cuts and ligase joins.
2. Do not mix them up.

Answer: (d) All of the above

Explanation:
1. DNA fingerprinting is used to determine identity and relationships, in forensic work and to study polymorphism.
2. So all of the above are correct.
3. Hence option (d) is correct: All of the above

Teacher's Note:
1. VNTR patterns are unique to each person except identical twins.