Number of chromosomes in a human cell is?

Appeared in: MNS 2015

Explanation

A normal human somatic (non-sex) cell contains 46 chromosomes.
These chromosomes are arranged in 23 pairs: 22 pairs of autosomes and one pair of sex chromosomes (XX for females, XY for males).
This is known as the diploid (2n) number, with one set of 23 chromosomes inherited from each parent.
Reproductive cells (gametes) are haploid (n) and contain only 23 chromosomes.

Option A: A count of 45 chromosomes is an aneuploidy (an abnormal number of chromosomes), not the standard number for a healthy human cell.
Option C: A count of 47 chromosomes is a form of aneuploidy called trisomy, where there is an extra chromosome.
Option D: A count of 48 chromosomes is a rare aneuploidy (e.g., tetrasomy) and is not the normal number for human cells. Interestingly, it is the normal chromosome number for potatoes.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Human Chromosome Number as background academic context rather than a clinical decision trigger.
Understanding the correct chromosome number is fundamental for genetic counseling and prenatal screening. Tests like amniocentesis or chorionic villus sampling are used to create a karyotype and detect aneuploidies.
Nurses play a key role in educating expectant parents about these screening tests and supporting families who receive a diagnosis of a chromosomal abnormality.
What if the question asked for the chromosome number in a human gamete? The answer would be 23, as gametes (sperm and egg cells) are haploid, containing only one set of chromosomes.

How to Approach the Question

Identify the core of the question: It asks for the standard 'number of chromosomes' in a 'human cell'.
Recognize this as a fundamental factual recall question from biology and genetics.
Recall that human somatic (body) cells are diploid (2n), meaning they have two sets of chromosomes.
Remember that the haploid number (n) for humans is 23. Therefore, the diploid number is 2 x 23 = 46.
Scan the options to find 46. The other options (45, 47, 48) represent abnormal chromosome numbers (aneuploidies) associated with genetic disorders.

Concept Tested & Keywords

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E6 Parks TextBook of Preventive & Social Medicine part 2 — Subpart B (pp 233-449 of 464) pp. 138-140, 137-139

E6 Pathology-Vandana Puri & Kavita Gaur Textbook of Pathology and Genetics p. 472-474

Practise the full MNS 2015

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