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Q7(b):
Describe the following:
(b) bivalent
Draw a diagram to illustrate your answer.
Solution :
Theoretical Definition of a Bivalent
A bivalent (also known as a tetrad) refers to the physical association of a pair of homologous chromosomes during the prophase I stage of meiosis [Per the Synapsis Process]. In this configuration, one chromosome is inherited from the male parent and the other from the female parent. The bivalent structure is stabilized by the synaptonemal complex, which facilitates precise alignment for potential genetic recombination [By the Mechanism of Crossing Over].
Structural Components of a Bivalent
- Homologous Pair: Two chromosomes of similar length, gene position, and centromere location.
- Sister Chromatids: Each chromosome consists of two identical sister chromatids connected at the centromere.
- Tetrad Configuration: Because each of the two homologous chromosomes consists of two sister chromatids, a single bivalent contains a total of four chromatids.
- Chiasmata: The visible points of connection where non-sister chromatids have undergone physical exchange of genetic material.
Visual Representation of a Bivalent
Functional Significance in Meiosis
| Process | Biological Outcome |
|---|---|
| Synapsis | Ensures accurate pairing of homologs [By Zygotene stage mechanics]. |
| Crossing Over | Results in genetic recombination, increasing variation in gametes [Per Mendel's Law of Independent Assortment]. |
| Alignment | Facilitates the orientation on the metaphase plate for segregation to opposite poles [Per Anaphase I kinetics]. |
Final Solution: A bivalent is a structural unit formed during Prophase I of meiosis, consisting of two homologous chromosomes (comprising four chromatids) held together by synapsis and often linked by at least one chiasma, essential for ensuring proper segregation and genetic diversity in sexually reproducing organisms.
More Questions from Class 11 Biology Cell Cycle and Division EXERCISES
- Q1: What is the average cell cycle span for a mammalian cell?
- Q2: Distinguish cytokinesis from karyokinesis.
- Q3: Describe the events taking place during interphase.
- Q4: What is $G_0$ (quiescent phase) of cell cycle?
- Q5: Why is mitosis called equational division?
- Q6(i): Name the stage of cell cycle at which one of the following events occur: (i) Chromosomes are moved to spindle equator.
- Q6(ii): Name the stage of cell cycle at which one of the following events occur: (ii) Centromere splits and chromatids separate.
- Q6(iii): Name the stage of cell cycle at which one of the following events occur: (iii) Pairing between homologous chromosomes takes place.
- Q6(iv): Name the stage of cell cycle at which one of the following events occur: (iv) Crossing over between homologous chromosomes takes place.
- Q7(a): Describe the following: (a) synapsis Draw a diagram to illustrate your answer.
- Q7(c): Describe the following: (c) chiasmata Draw a diagram to illustrate your answer.
- Q8: How does cytokinesis in plant cells differ from that in animal cells?
- Q9: Find examples where the four daughter cells from meiosis are equal in size and where they are found unequal in size.
- Q10: Distinguish anaphase of mitosis from anaphase I of meiosis.
- Q11: List the main differences between mitosis and meiosis.
- Q12: What is the significance of meiosis?
- Q13(i): Discuss with your teacher about (i) haploid insects and lower plants where cell-division occurs, and
- Q13(ii): Discuss with your teacher about (ii) some haploid cells in higher plants where cell-division does not occur.
- Q14: Can there be mitosis without DNA replication in ‘S’ phase?
- Q15: Can there be DNA replication without cell division?
- Q16(i): Analyse the events during every stage of cell cycle and notice how the following two parameters change (i) number of chromosomes ($N$) per cell
- Q16(ii): Analyse the events during every stage of cell cycle and notice how the following two parameters change (ii) amount of DNA content ($C$) per cell
CBSE Solutions for Class 11 Biology Cell Cycle and Division
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
- Cell – The Unit of Life
- Biomolecules
- 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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