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Question 572
Genetics → General
Classification
Question
SSBAOptions
Explanation
A central centromere with equal arms identifies the first chromosome as metacentric. The second is acrocentric: its centromere is near one end and its p arm is very short but remains present. This retained short arm distinguishes an acrocentric chromosome from the terminal-centromere configuration described as telocentric. Telocentric chromosomes are not present in normal human cells.
Option Validity
A) The first classification is correct, but a submetacentric chromosome has only a moderately unequal pair of arms, rather than the very short p arm described.
B) A submetacentric centromere is off-centre, whereas the first chromosome has equal arms; the second does not have the central centromere required for a metacentric chromosome.
C) The first chromosome has a central rather than near-terminal centromere. The demonstrably present p arm of the second also argues against the telocentric description.
D) The second classification is correct, but the first chromosome has two equal arms and a central centromere, not a terminal centromere.
Further Reading
Saxena R. Textbook for MRCOG-1: Basic Sciences in Obstetrics and Gynaecology. Jaypee Brothers Medical Publishers; 2016. Chapter 8, Genetics: Human Chromosomes. Printed pages 256–257.