Which among the following is the smallest Human Chromosome?

Appeared in: NHM UP Staff Nurse-2021 Shift-1st

Explanation

Chromosome 21 is the smallest human autosome (non-sex chromosome), containing approximately 48 million base pairs of DNA.
Human chromosomes are numbered roughly in order of decreasing size, from the largest (Chromosome 1) to the smallest.
A historical error in microscopic measurement led to Chromosome 21 being numbered before Chromosome 22, even though it was later found to be smaller.
Among the given options, Chromosome 21 has the highest number and is factually the smallest in size.

Option A: Chromosome 10 is a medium-sized chromosome, containing about 133 million base pairs, which is significantly larger than Chromosome 21.
Option B: Chromosome 16 is larger than Chromosome 21, with approximately 90 million base pairs.
Option C: Chromosome 20 is a small chromosome but is still larger than Chromosome 21, containing about 64 million base pairs.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Human karyotyping and chromosome nomenclature as background academic context rather than a clinical decision trigger.
Knowledge of chromosome structure is fundamental for nurses to understand the basis of genetic disorders and counseling.
The most common chromosomal disorder compatible with life is Trisomy 21 (Down syndrome), caused by an extra copy of Chromosome 21. Its relatively high incidence and survival rate are partly due to the small size and low gene density of this chromosome.
Nurses play a key role in supporting families and providing care for individuals with Down syndrome, from prenatal screening discussions to lifelong health management.

How to Approach the Question

Identify the core question: The question asks to identify the smallest chromosome from a given list.
Recall the general principle of human chromosome numbering: Chromosomes are numbered 1 through 22, generally from largest to smallest.
Access specific knowledge: Remember the key exception to this rule – Chromosome 21 is actually smaller than Chromosome 22.
Evaluate the options: The options are Chromosomes 10, 16, 20, and 21. Based on the numbering principle, higher numbers correspond to smaller sizes.
Synthesize and conclude: Chromosome 21 is the highest-numbered autosome in the list and is known to be the smallest autosome. Therefore, it is the correct answer.

Concept Tested & Keywords

Q6CRxdRKYSHGQEJfZiTHRU

E6 Anatomy Grays 43e Vol 1 Part 1 p. 45-47

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 805-807

Practise the full NHM UP Staff Nurse-2021 Shift-1st

Attempt every question from this paper in a timed mock, then review the full solution for each one.