Q40. Mesenchymal stromal cells are associated most clearly with formation of:
[State PSC — Practice]
- (a) Viruses and bacteriophages
- (b) Every type of plant leaf
- (c) Only mature neurons without restriction
- (d) Bone, cartilage and fat lineages under suitable conditions
Answer: (d) Bone, cartilage and fat lineages under suitable conditions
Explanation: Mesenchymal stromal cells are multipotent stromal populations studied in bone marrow and other tissues. Under appropriate conditions they can show osteogenic, chondrogenic and adipogenic differentiation. Claims of universal cures from such cells are not scientifically justified.
Q39. The cell formed by fusion of sperm and ovum is generally:
[UPSC CSE — Practice]
- (a) Haploid mature gamete
- (b) A pollen tube
- (c) Diploid zygote
- (d) A bacterial spore
Answer: (c) Diploid zygote
Explanation: Fertilisation combines haploid genetic contributions from two gametes and normally restores diploidy in the zygote. Early divisions occur through mitosis. Chromosome-number abnormalities can arise, but the usual human zygote contains 46 chromosomes.
Q38. Amniocentesis obtains diagnostic material primarily from:
[WBCS — Practice]
- (a) A placental blood vessel without fluid sampling
- (b) Amniotic fluid surrounding the fetus
- (c) The mother’s lens of the eye
- (d) An adult’s bone marrow
Answer: (b) Amniotic fluid surrounding the fetus
Explanation: Amniocentesis samples amniotic fluid containing fetal cells and other biological material. Analyses can assess selected chromosomal and genetic disorders. The procedure involves medical risk, requires informed consent and is subject to laws regulating prenatal testing.
Q37. The enzyme commonly described as the “molecular stitcher” in recombinant DNA technology is:
[RAS / RPSC (Pre) 2013]
- (a) DNA ligase
- (b) DNA helicase
- (c) Restriction endonuclease
- (d) RNA polymerase
Answer: (a) DNA ligase
Explanation: DNA ligase forms phosphodiester bonds to seal breaks between compatible DNA ends. Restriction endonucleases cut DNA, while ligases join the resulting fragments. Both enzyme classes underpin conventional recombinant DNA construction and molecular cloning.
Q36. In India, prenatal tests for selecting a child’s sex are:
[MPPSC — Practice]
- (a) Equivalent to routine vaccination
- (b) An unrestricted household service
- (c) Required in every pregnancy
- (d) Restricted and prohibited for sex selection under relevant law
Answer: (d) Restricted and prohibited for sex selection under relevant law
Explanation: India’s Pre-Conception and Pre-Natal Diagnostic Techniques law prohibits sex selection and regulates prenatal diagnostic techniques. Medical investigations may be justified for legitimate clinical indications, but using them to disclose or select fetal sex is unlawful.
Q35. What is the defining feature of tissue-specific adult stem cells?
[UPPCS — Practice]
- (a) They have no ability to divide
- (b) They exist only before fertilisation
- (c) They replenish particular cell lineages within tissues
- (d) They always generate an entire embryo
Answer: (c) They replenish particular cell lineages within tissues
Explanation: Adult or somatic stem cells help maintain and repair specific tissues. Examples include blood-forming and intestinal stem cells. Their normal differentiation ranges are narrower than those of embryonic pluripotent stem cells, though plasticity depends on cell type.
Q34. Dolly the sheep was produced using which main technique?
[RAS / RPSC — Practice]
- (a) Ordinary cross-pollination
- (b) Somatic cell nuclear transfer
- (c) Artificial selection alone
- (d) Bacterial conjugation
Answer: (b) Somatic cell nuclear transfer
Explanation: Dolly was produced by transferring the nucleus of a differentiated adult cell into an enucleated egg, followed by embryonic development and implantation. Born in 1996, she demonstrated that an adult nucleus could be reprogrammed for mammalian development.
Q33. Bacillus thuringiensis is used in agriculture primarily as a source of what?
[Uttarakhand PCS (Pre) 2012]
- (a) Biological insecticide
- (b) Nitrogen-fixing biofertiliser
- (c) Phosphate solvent
- (d) Chemical weed killer
Answer: (a) Biological insecticide
Explanation: Bacillus thuringiensis produces insecticidal crystal proteins called Cry toxins. Appropriate Bt formulations can target susceptible insect pests, and selected cry genes have been engineered into crops such as cotton. It is not principally a nitrogen-fixing biofertiliser.
Q32. Why was Dolly considered a landmark in reproductive biotechnology?
[SSC CGL — Practice]
- (a) She was the first mammal ever born
- (b) Her DNA was entirely synthetic
- (c) She grew without an egg cell
- (d) She developed from the nucleus of an adult somatic cell
Answer: (d) She developed from the nucleus of an adult somatic cell
Explanation: Dolly was the first mammal cloned successfully from an adult somatic-cell nucleus. Earlier mammalian cloning had used embryonic cells. Her birth provided evidence that differentiated nuclei retain information needed to direct development after suitable reprogramming.
Q31. An enucleated ovum is one from which scientists have removed the:
[SSC CHSL — Practice]
- (a) Mitochondria in every case
- (b) Extracellular water only
- (c) Nuclear genetic material
- (d) Cell membrane entirely
Answer: (c) Nuclear genetic material
Explanation: In somatic cell nuclear transfer, the recipient egg normally has its own nuclear chromosomes removed. An introduced donor nucleus is then exposed to egg cytoplasm, which can reprogramme gene expression and support initial embryonic development.
