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Question 580

Genetics → General

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Type SSBA

UUID 7a048fb2-3840-48c6-a4c2-b16da05c8cc3

Classification

Speciality

Obstetrics and Gynaecology

Group

Basic

Title

Genetics

Topic

General

Subtopic 1

Human Chromosomes

Subtopic 2

Chromosome examination

Subtopic 3

Metaphase preparation and Q-banding

Question Type

SBA

Question

SSBA

Question Header

Question Stem

A laboratory needs a chromosome preparation from normally dividing human cells. It must first obtain cells at the stage used for karyotype analysis. It must then distinguish two normal chromosomes that are similar in overall size and shape by comparing their banding patterns.

Options

A Arrest with colchicine at metaphase, then compare unbanded chromosomes by arm length alone

B Arrest with colchicine at interphase, then apply quinacrine fluorescence banding

C Arrest with colchicine at metaphase, then apply quinacrine fluorescence banding

D Use quinacrine to arrest the cells at metaphase, then use colchicine to produce fluorescent bands

E Count peripheral chromatin bodies in interphase buccal cells, then compare those bodies by size

Explanation

Colchicine is used to arrest dividing cells at metaphase for karyotype analysis. Q-banding uses the fluorescent stain quinacrine to reveal chromosome-specific patterns, allowing chromosomes of similar size and shape to be distinguished. The two steps serve different purposes: obtaining the appropriate division stage and resolving chromosome identity by banding.

Option Validity

A) The preparation step is correct, but unbanded arm-length comparison does not supply the requested banding-pattern distinction between similar chromosomes.

B) Quinacrine is appropriate for Q-banding, but metaphase, not interphase, is the arrest stage used for the chromosome preparation.

D) The functions of the agents are reversed. Colchicine provides the metaphase arrest; quinacrine provides the fluorescent banding.

E) Peripheral chromatin bodies in buccal cells concern sex chromatin rather than a metaphase chromosome preparation with Q-banding.

Source & metrics

Authored Difficulty

5.00

Evaluation Score

—

Destination

Site

Source

Saxena - MRCOG-1 Basic Sciences - Genetics

Source Section

Chapter 8 — Genetics — Human Chromosomes; X Chromosome

Source Locator

Printed pages 256–258

Updated

2026-10-06 01:57:35

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