Selected MCQ

Current Question
Down syndrome (trisomy 21) results in how many total chromosomes in a karyotype?
  • A. 45
  • B. 46
  • C. 47
  • D. 48
Correct Answer: C
Explanation:
Down syndrome is caused by an extra copy of chromosome 21. Humans normally have 46 chromosomes; trisomy adds one extra, making 47.
Related Question 1
Nucleosomes are composed of DNA wrapped around an octamer of histones. How many base pairs of DNA are wrapped around one nucleosome core?
  • A. ~50 bp
  • B. ~146 bp
  • C. ~300 bp
  • D. ~10 bp
Correct Answer: B
Explanation:
About 146 base pairs of DNA wrap ~1.7 turns around the histone octamer (2 copies each of H2A, H2B, H3, H4) in a nucleosome core.
Related Question 2
Inheritance of human height, which is influenced by many genes and environmental factors, is an example of:
  • A. Codominance
  • B. Polygenic inheritance
  • C. Pleiotropy
  • D. Autosomal dominance
Correct Answer: B
Explanation:
Height is a quantitative trait determined by multiple genes (polygenes) and the environment, consistent with polygenic inheritance.
Related Question 3
Phospholipase C (PLC) activation results in the generation of which second messenger that releases Ca²⁺ from the endoplasmic reticulum?
  • A. cAMP
  • B. cGMP
  • C. IP₃
  • D. DAG
Correct Answer: C
Explanation:
PLC cleaves PIP₂ into IP₃ and DAG. IP₃ diffuses to the ER, causing Ca²⁺ release, while DAG activates PKC.
Related Question 4
During the eukaryotic cell cycle, which checkpoint ensures that all chromosomes are correctly attached to the mitotic spindle before proceeding to anaphase?
  • A. G1/S checkpoint
  • B. G2/M checkpoint
  • C. Spindle (metaphase) checkpoint
  • D. S-phase checkpoint
Correct Answer: C
Explanation:
The spindle assembly (metaphase) checkpoint monitors attachment of all kinetochores to spindle microtubules. It prevents the onset of anaphase until all chromosomes are properly aligned and attached.
Related Question 5
Which cell cycle checkpoint is specifically responsible for preventing the onset of anaphase until all chromosomes are properly attached to the spindle apparatus?
  • A. G1/S checkpoint
  • B. G2/M checkpoint
  • C. Spindle assembly (metaphase) checkpoint
  • D. DNA damage checkpoint
Correct Answer: C
Explanation:
The spindle assembly (metaphase) checkpoint delays anaphase until every chromosome is correctly attached to the mitotic spindle, ensuring accurate chromosome segregation.