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Question 575

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Classification

Speciality

Obstetrics and Gynaecology

Group

Basic

Title

Genetics

Topic

General

Subtopic 1

Human Sex Chromosomes

Subtopic 2

Y Chromosome

Subtopic 3

SRY Function

Question Type

SBA

Question

SSBA

Question Header

Question Stem

An experimental model compares three otherwise matched preparations during gonadal development. Preparation 1 receives a small Y-derived DNA fragment containing an intact SRY gene and develops testicular tissue. Preparation 2 receives a much larger Y-derived fragment in which SRY alone has been rendered non-functional and does not develop testicular tissue. Preparation 3 is identical to preparation 2 except that SRY function is restored; testicular tissue now develops. Restoring SRY does not change the amount of Y-derived DNA present.

Options

A Testicular development depends chiefly on the total amount of Y-derived DNA

B The remaining Y-derived sequences are sufficient for testicular development when SRY is inactive

C The presence of any Y-derived fragment establishes testicular development irrespective of its gene function

D Functional SRY, normally located on the short arm of Y, is the discriminating factor for testicular development in these preparations

E An intact whole Y chromosome is required even when the SRY gene is functional

Explanation

The small SRY-containing fragment shows that an intact whole Y chromosome is not required in this model. Failure of the larger fragment when SRY is inactive argues against total Y-derived DNA or its remaining sequences being sufficient. Restoration of development when SRY function alone is restored provides the decisive comparison. Together these observations support a specific functional role for SRY, which is located on the short arm of Y and elicits testicular development.

Option Validity

A) The small fragment supports development while the larger SRY-inactivated fragment does not; restoring function changes the outcome without increasing DNA amount.

B) Preparation 2 retains the other Y-derived sequences yet lacks testicular development when SRY is non-functional.

C) Preparation 2 contains Y-derived DNA but does not develop testicular tissue, so sequence presence alone is insufficient.

E) Preparation 1 develops testicular tissue with only a small SRY-containing fragment, which contradicts a requirement for an intact whole Y chromosome.

Source & metrics

Authored Difficulty

6.00

Evaluation Score

—

Destination

Site

Source

Saxena - MRCOG-1 Basic Sciences - Genetics

Source Section

Chapter 8 — Genetics; Human Sex Chromosomes; Y Chromosome

Source Locator

Printed page 258

Updated

2026-10-06 01:57:35

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