Sample 1Medium
A figure shows a chromosome at metaphase, made of two sister chromatids joined at the primary constriction. The primary constriction lies close to one end, so the chromosome has one extremely short arm and one very long arm. What is this type of chromosome called?
- A
Acrocentric
- B
Metacentric
- C
Sub-metacentric
- D
Telocentric
Show the answer
The answer is A.Chromosomes are classed by the position of the centromere. When it lies close to one end, giving one extremely short and one very long arm, the chromosome is acrocentric.
- B.
A metacentric chromosome has the centromere in the middle, forming two equal arms.
- C.
A sub-metacentric chromosome has the centromere slightly away from the middle, so one arm is only somewhat shorter than the other.
- D.
A telocentric chromosome has a terminal centromere, at the very end of the chromosome.
NCERT: Class 11 Biology, Chapter 8
Sample 2NEET level
Consider the following statements about chromosomes: I. Every chromosome has a primary constriction, the centromere, with disc-shaped kinetochores on its sides. II. A metacentric chromosome has a middle centromere forming two equal arms. III. A sub-metacentric chromosome has a terminal centromere. IV. An acrocentric chromosome has its centromere close to one end, forming one extremely short and one very long arm. Which of the statements above are correct?
- A
I and II only
- B
I, II and IV only
- C
II, III and IV only
- D
I, II, III and IV
Show the answer
The answer is B.Every chromosome has a centromere bearing kinetochores; metacentric chromosomes have a middle centromere and acrocentric ones have it close to an end. In a sub-metacentric chromosome the centromere is slightly away from the middle; a terminal centromere describes a telocentric chromosome, so III is wrong.
- A.
Leaves out IV, which correctly describes an acrocentric chromosome.
- C.
Includes the wrong III and leaves out the correct I.
- D.
Includes III: a terminal centromere is telocentric, not sub-metacentric.
NCERT: Class 11 Biology, Chapter 8 (Cell: The Unit of Life), Nucleus