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Q14:
What is a centromere? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing the position of centromere on different types of chromosomes.
Solution :
Definition of Centromere
A centromere is a specialized, condensed region of a chromosome that links a pair of sister chromatids together. During the mitotic and meiotic cell divisions, the centromere acts as the site of attachment for the kinetochore—a complex of proteins that binds to spindle fibers [Per the Chromosome Theory of Inheritance]. The primary function of the centromere is to ensure the proper segregation of chromosomes into daughter cells by facilitating the movement of chromatids toward opposite poles during anaphase.
Classification Based on Centromere Position
Chromosomes are classified based on the relative position of the centromere, which divides the chromosome into two arms of varying lengths, referred to as the $p$ arm (short) and $q$ arm (long). The four primary categories are as follows:
| Chromosome Type | Centromere Position | Appearance in Anaphase |
|---|---|---|
| Metacentric | Median (middle of the chromosome) | V-shaped |
| Sub-metacentric | Sub-median (slightly away from the middle) | L-shaped |
| Acrocentric | Sub-terminal (near the end) | J-shaped |
| Telocentric | Terminal (at the very tip) | I-shaped |
Visual Representation of Chromosome Types
Analytical Summary of Chromosome Morphology
- Metacentric: The centromere is exactly in the center, resulting in two arms of equal length. [Based on geometric symmetry].
- Sub-metacentric: The centromere position creates one slightly shorter arm and one longer arm.
- Acrocentric: The centromere is situated close to one end, resulting in an extremely short arm and a very long arm.
- Telocentric: The centromere occupies the terminal end of the chromosome, which is a state typically observed in specific organisms but rare in humans.
Final Solution: The centromere is a constricted primary region of the chromosome that acts as the anchor for spindle fibers; its variable positioning (median, sub-median, sub-terminal, and terminal) dictates the structural morphology (Metacentric, Sub-metacentric, Acrocentric, and Telocentric) of the chromosome.
More Questions from Class 11 Biology Cell – The Unit of Life EXERCISES
- Q1: Which of the following is not correct?
- Q2: New cells generate from
- Q3: Match the following Column I Column II (a) Cristae (i) Flat membranous sacs in stroma (b) Cisternae (ii) Infoldings in mitochondria (c) Thylakoids (iii) Disc-shaped sacs in Golgi apparatus
- Q4: Which of the following is correct:
- Q5: What is a mesosome in a prokaryotic cell? Mention the functions that it performs.
- Q6: How do neutral solutes move across the plasma membrane? Can the polar molecules also move across it in the same way? If not, then how are these transported across the membrane?
- Q7: Name two cell-organelles that are double membrane bound. What are the characteristics of these two organelles? State their functions and draw labelled diagrams of both.
- Q8: What are the characteristics of prokaryotic cells?
- Q9: Multicellular organisms have division of labour. Explain.
- Q10: Cell is the basic unit of life. Discuss in brief.
- Q11: What are nuclear pores? State their function.
- Q12: Both lysosomes and vacuoles are endomembrane structures, yet they differ in terms of their functions. Comment.
- Q13(i): Describe the structure of the following with the help of labelled diagrams. (i) Nucleus
- Q13(ii): Describe the structure of the following with the help of labelled diagrams. (ii) Centrosome
CBSE Solutions for Class 11 Biology Cell – The Unit of Life
Chapters in CBSE - Class 11 Biology
- The Living World
- Biological Classification
- Plant Kingdom
- Animal Kingdom
- Morphology of Flowering Plants
- Anatomy of Flowering Plants
- Structural Organisation in Animals
- Biomolecules
- Cell Cycle and Division
- Transport in Plants
- Mineral Nutrition
- Photosynthesis
- Respiration in Plants
- Plant Growth and Development
- Digestion and Absorption
- Breathing and Exchange of Gases
- Body Fluids and Circulation
- Excretory Products and Elimination
- Locomotion and Movement
- Neural Control and Coordination
- Chemical Coordination and Integration
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