Free Chromosomes MCQs with Answers
633 Chromosomes MCQs from Biology, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Chromosomes are DNA-protein structures that carry genes and become visible during cell division. Coverage includes chromatin, centromeres, sister chromatids, homologous chromosomes, chromosome number, and the distinction between diploid and haploid cells, with links to DNA replication, mitosis and meiosis.
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633 questions · page 3 of 32
- A. Down's syndrome
- B. Klinifelter's syndrome
- C. Turner's syndrome
- D. Jacob's syndrome
Explanation: Down syndrome is usually caused by trisomy 21, meaning there are three copies of autosomal chromosome 21.
Correct answer: Down's syndrome- A. Chromatin
- B. Kinetochore
- C. Chromatid
- D. Centromere
Explanation: After DNA replication, each chromosome consists of two identical sister chromatids joined at the centromere until they separate during…
Correct answer: Chromatid- A. Karyokinesis
- B. Cytokinesis
- C. Interphase
- D. Both a & b
Explanation: Mitosis is commonly considered to include karyokinesis, the division of the nucleus, followed by cytokinesis, the division of the…
Correct answer: Both a & b- A. Chromatid
- B. Centromere
- C. Kinetochore
- D. Arms
Explanation: After DNA replication, each identical copy of a chromosome is called a sister chromatid, and the two chromatids remain joined at the…
Correct answer: Chromatid- A. DNA replicates by semiconservative replication
- B. Cyanobacteria were responsible for the oxygenation of the atmosphere
- C. The early atmosphere was composed of ammonia and methane
- D. Organic molecules can arise from inorganic precursor
Explanation: Stanley Miller and Harold Urey simulated early Earth's atmosphere (methane, ammonia, hydrogen, and water vapor) and passed electric sparks…
Correct answer: Organic molecules can arise from inorganic precursor- A. Duplex, Helix
- B. Helix, Duplex
- C. Duplex, Duplex
- D. Helix, Helix
Explanation: In semi-conservative replication, each new DNA double helix (duplex) contains one parental and one new strand.
Correct answer: Duplex, Duplex- A. Small ribosomal subunit
- B. Initiation factor
- C. Elongation factor
- D. Large ribosomal subunit
Explanation: The large ribosomal subunit (60S in eukaryotes, 50S in prokaryotes) contains the peptidyl transferase activity that catalyzes peptide bond…
Correct answer: Large ribosomal subunit- A. Aminoacyl site
- B. Exit site
- C. Peptidyl site
- D. E site
Explanation: The P site (Peptidyl site) of the ribosome holds the tRNA carrying the growing polypeptide chain and is the site of peptide bond formation.
Correct answer: Peptidyl site- A. 331
- B. 993
- C. 93
- D. 330
Explanation: Each codon = 3 nucleotides → 993 ÷ 3 = 331 codons. One is a stop codon → 330 codons code for amino acids.
Correct answer: 330- A. GUA
- B. UAA
- C. UUG
- D. AGU
Explanation: UAA, UAG, and UGA are stop codons. They do not code for any amino acid, instead signal termination of translation.
Correct answer: UAA51. In what direction can a DNA polymerase work when catalyzing the addition of nucleotide monomers?
- A. From the 5' toward the 3' end of the new strand
- B. From the replication centers in two directions called replication forks
- C. From the 3' to the 5' end of the strand being assembled
- D. In both directions if DNA ligase is present
Explanation: DNA polymerase adds nucleotides to the 3′-OH end, meaning the new strand grows in the 5′ → 3′ direction.
Correct answer: From the 5' toward the 3' end of the new strand- A. 4
- B. 16
- C. 8
- D. 64
Explanation: Each codon = 3 bases. With 2 possible nucleotides (A and C): 2³ = 8 codons.
Correct answer: 8- A. DNA proof‑reading
- B. DNA repair
- C. Unwinding
- D. Annealing
Explanation: DNA polymerase I has 3′ → 5′ exonuclease activity allowing proofreading and correction of errors in the new strand.
Correct answer: DNA proof‑reading- A. Calcium chloride
- B. Cesium chloride
- C. Calcium carbide
- D. Silicon carbide
Explanation: Meselson and Stahl used density gradient centrifugation in CsCl with isotopes of nitrogen (¹⁵N and ¹⁴N) to prove semi conservative DNA…
Correct answer: Cesium chloride- A. Addition of primer
- B. Unwinding
- C. Polymerization
- D. Rewinding
Explanation: Helicase unwinds the double helix, separating the strands to allow replication.
Correct answer: Unwinding- A. Adenine and guanine
- B. Cytosine and uracil
- C. Cytosine and guanine
- D. All of the above
Explanation: The genetic code includes all 4 bases (A, U/T, G, C) in different triplet combinations to form codons.
Correct answer: All of the above- A. Serine and isoleucine
- B. Cysteine and valine
- C. Tyrosine and tryptophan
- D. Phenylalanine and methionine
Explanation: Har Gobind Khorana used synthetic RNA to decipher codons. He first identified codons for cysteine (UGU, UGC) and valine (GUU, GUC, GUA…
Correct answer: Cysteine and valine- A. DNA polymerase
- B. Topoisomerase
- C. Unwindase/helicase
- D. Gyrase
Explanation: Helicase separates the two DNA strands by breaking hydrogen bonds.
Correct answer: Unwindase/helicase- A. tRNA
- B. mRNA
- C. rRNA
- D. both (B) and (C)
Explanation: Anticodons are present on tRNA and are complementary to codons on mRNA during translation.
Correct answer: tRNA60. If the sequence of bases in DNA is ATTCGATG, then the sequence of bases in its transcript will be:
- A. GUAGCUUA
- B. AUUCGAUG
- C. CAUCGAAU
- D. UAAGCUAC
Explanation: In transcription, complementary mRNA is formed. A → U, T → A, C → G, G → C. Hence, ATTCGATG → UAAGCUAC.
Correct answer: UAAGCUAC