Practise 34 real Federal Board questions on Chromosomes and DNA from 2023 to 2026. See the answer and explanation as soon as you answer.
Chromosomes and DNA is one of the 15 main chapters in our Federal Board FSC Biology question bank (11th and 12th class), and about 7% of its real questions come from it. Tayyari Karo has 34 real questions on this chapter from 2023 to 2026; 11 are multiple choice and marked instantly, and the rest are short and long questions with a model answer. By difficulty: 27 medium, 6 hard, 1 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
Griffith and Hershey-Chase experiments proved that:
Answer: B. DNA is hereditary material
Griffith's transformation experiment and the Hershey–Chase blender experiment (using labelled phage DNA vs protein) together established DNA, not protein, as the hereditary material.
When RNA polymerase binds to promoter for transcription, the unit which detaches from it after initiation is:
Answer: C. γ (Gamma)
The RNA polymerase holoenzyme's initiation-factor subunit dissociates from the core enzyme once transcription is successfully initiated, allowing elongation to proceed.
The semi-conservative model of DNA replication was experimentally proven by:
Answer: C. Meselson and Stahl
Meselson and Stahl's ¹⁵N/¹⁴N density-gradient experiment on E. coli directly demonstrated semi-conservative DNA replication.
RNA lacks:
Answer: C. Thymine
RNA contains adenine, guanine, cytosine and uracil (instead of thymine); thymine is found only in DNA.
Phosphodiester bond is:
Answer: B. C-O-P-O-C
A phosphodiester bond links the 3' carbon of one sugar to the 5' carbon of the next sugar through a phosphate group, giving the linkage sugar–O–P–O–sugar (C-O-P-O-C).
Select the palindromic sequence in the given fragment of DNA (5'-AGAATTGC-3' / 3'-TCTTAACG-5'):
Answer: B. AA TT / TT AA
A palindromic DNA sequence reads the same 5'→3' on both strands; AATT paired with its direct complement TTAA satisfies this (its reverse complement is again AATT), the hallmark of many restriction-enzyme recognition sites.
State three conclusions of Griffith's control experiments.
(1) Live R-strain (non-virulent) bacteria alone do not kill the mouse, confirming the R strain is harmless.
(2) Heat-killed S-strain (virulent) bacteria alone also do not kill the mouse, confirming that heat destroys the bacteria's disease-causing ability.
(3) Live S-strain bacteria alone do kill the mouse, confirming that the S strain itself is virulent/pathogenic — these controls set up the key result that a mixture of heat-killed S + live R together does kill the mouse, indicating 'transformation' had occurred.
Write three major steps involved in DNA sequences.
Three major steps of (Sanger) DNA sequencing: (1) The DNA sample is denatured into single strands and mixed with primers, DNA polymerase, normal deoxynucleotides (dNTPs) and a small proportion of fluorescently/radioactively labelled chain-terminating dideoxynucleotides (ddNTPs). (2) DNA polymerase synthesises new complementary strands of varying lengths, each terminating wherever a ddNTP is randomly incorporated, generating fragments of every possible length ending in a labelled base. (3) These fragments are separated by size using gel electrophoresis (or capillary electrophoresis), and the sequence is read off from the order of the labelled terminal bases, smallest to largest fragment.
| Session | Questions |
|---|---|
| 2026 Annual | 5 |
| 2025 1st Annual | 10 |
| 2025 2nd Annual | 9 |
| 2024 Annual | 5 |
| 2023 Annual | 5 |
34 real Federal Board (FBISE) Biology questions on Chromosomes and DNA from 2023 to 2026, for 11th and 12th class. Each one shows the session it came from.
No. We could not find an official FBISE marking scheme for these papers, so the answers and explanations are written by Tayyari Karo for practice. Check anything important with your teacher or textbook.
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