Q50. A rare genetic disorder makes the hard matrix of bone less rigid, leading to frequent fractures. Which explanation is most likely?
[RRB Group D – 17 Aug 2026, Shift 2]
(A) Loss of sugars from cartilage
(B) Reduced plasma proteins
(C) A type I collagen defect due to mutations in COL1A1 or COL1A2
(D) Excess haemoglobin in bones
Answer: (C) A type I collagen defect due to mutations in COL1A1 or COL1A2
Explanation: Osteogenesis imperfecta, or brittle-bone disease, frequently involves defects in type I collagen. The collagen framework gives bone tensile strength, while minerals provide hardness. Faulty collagen therefore makes bones fracture easily even when mineral content is not the primary problem.
Q49. How many chromosomes should a normal human zygote contain?
[RRB Group D – 11 Aug 2026, Shift 1]
(A) 92
(B) 69
(C) 23
(D) 46
Answer: (D) 46
Explanation: A human sperm and ovum each carry 23 chromosomes. Their fusion restores the diploid complement of 46 in the zygote. Abnormal fertilisation or chromosome segregation can produce numerical variations, including trisomies and monosomies linked with genetic syndromes.
Q48. BRIC-InStem, Bengaluru, collaborated with which institution on India’s indigenous gene-therapy research for haemophilia?
[RRB NTPC (UG) – 7 May 2026, Shift 3]
(A) Christian Medical College, Vellore
(B) Gandhi Medical College, Hyderabad
(C) AIIMS, New Delhi
(D) ICMR headquarters
Answer: (A) Christian Medical College, Vellore
Explanation: Christian Medical College, Vellore, and BRIC-InStem collaborated on gene-therapy research for haemophilia. Haemophilia A results from deficient or defective clotting factor VIII. Gene therapy aims to enable cells to produce the missing functional protein, reducing bleeding episodes.
Q47. What is the main purpose of a Punnett square in genetics?
[RRB NTPC (Graduate) – 17 Mar 2026, Shift 2]
(A) Determining the phenotype with certainty
(B) Locating a gene on a chromosome
(C) Predicting possible outcomes of genetic crosses
(D) Sequencing DNA molecules
Answer: (C) Predicting possible outcomes of genetic crosses
Explanation: A Punnett square displays possible allele combinations contributed by parents. It predicts probabilities, not guaranteed individual outcomes. The tool is particularly useful for estimating carrier and affected-offspring risks in simple Mendelian disorders such as sickle-cell anaemia or haemophilia.
Q46. Which meiotic error is a common cause of trisomy 21?
(A) Crossing over
(B) Nondisjunction
(C) Transcription
(D) DNA methylation
Answer: (B) Nondisjunction
Explanation: Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate correctly during cell division. A gamete may consequently contain an extra chromosome 21. After fertilisation, the resulting embryo can have three copies and develop Down syndrome.
Q45. Which term describes gain or loss of one or a few chromosomes rather than an entire set?
(A) Polyploidy
(B) Aneuploidy
(C) Euploidy
(D) Conjugation
Answer: (B) Aneuploidy
Explanation: Aneuploidy changes the number of individual chromosomes, producing conditions such as monosomy or trisomy. Polyploidy, by contrast, changes the number of entire chromosome sets. Human Down, Turner and Klinefelter syndromes are examples of clinically important aneuploid conditions.
Q44. What is the chromosomal formula of monosomy in a diploid organism?
(A) 2n + 1
(B) 3n
(C) 2n − 1
(D) 4n
Answer: (C) 2n − 1
Explanation: Monosomy means that one member of an otherwise normal chromosome pair is missing. It is represented by 2n − 1; in humans, 45,X is a well-known example. The loss alters gene dosage and can affect normal growth and development.
Q43. A chromosomal segment breaks, rotates through 180 degrees and reattaches to the same chromosome. What is this?
(A) Deletion
(B) Duplication
(C) Inversion
(D) Translocation
Answer: (C) Inversion
Explanation: An inversion reverses the orientation of a chromosomal segment after breakage and rejoining. It need not change the total amount of DNA, although a breakpoint may disrupt genes and inverted regions can complicate chromosome pairing during meiosis.
Q42. Loss of a segment from a chromosome is called which structural aberration?
(A) Deletion
(B) Duplication
(C) Inversion
(D) Reciprocal translocation
Answer: (A) Deletion
Explanation: Deletion removes part of a chromosome and the genes contained within that segment. Consequences depend on the location and size of the missing region. Loss of genetic material may impair development because affected genes are present in insufficient copies.
Q41. Repeating a chromosome segment so that extra copies are present is termed what?
(A) Monosomy
(B) Duplication
(C) Inversion
(D) Nondisjunction
Answer: (B) Duplication
Explanation: Duplication increases the number of copies of a chromosomal region. This can disturb normal gene dosage and lead to disease. Some forms of Charcot–Marie–Tooth neuropathy, for example, result from duplication of a segment containing the PMP22 gene.