Numerical changes in chromosomes ( Polyploidy ) || BSc 3rd year Botany 6th Semester 1st Semester 

Описание: Chapter 6: Numerical Changes in Chromosomes – Polyploidy

B.Sc. Third Year | Botany | Sixth Semester
Paper: Cytogenetics, Plant Breeding and Nanotechnology

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1. Introduction to Polyploidy
• Polyploidy is a type of numerical chromosomal variation.
• It refers to the presence of more than two complete sets of chromosomes in an organism.
• Normal diploid organisms contain two sets of chromosomes (2n).
• Polyploid organisms may have:
• Triploid (3n)
• Tetraploid (4n)
• Hexaploid (6n)
• Polyploidy is very common in plants and rare in animals.
• It plays a major role in plant evolution and crop improvement.

2. Causes of Polyploidy
• Polyploidy occurs due to abnormal cell division.
• Main causes include:
• Failure of spindle fiber formation during meiosis or mitosis
• Formation of unreduced (2n) gametes
• Fusion of unreduced gametes during fertilization
• Artificial polyploidy can be induced by:
• Colchicine treatment
• Temperature shock
• Chemical inhibitors of mitotic spindle

3. Types of Polyploidy

Polyploidy is mainly classified into two types:

A. Autopolyploidy
• Chromosome sets originate from a single species.
• All chromosome sets are genetically similar.
• Meiosis is often irregular due to multivalent formation.
• Fertility is usually reduced.
• Morphological features include:
• Large cell size
• Thick leaves
• Bigger fruits
• Examples:
• Potato (Solanum tuberosum)
• Alfalfa
• Banana


B. Allopolyploidy
• Formed by hybridization between two different species.
• Followed by chromosome doubling.
• Chromosome sets are from different species.
• Regular meiosis occurs due to pairing of homologous chromosomes.
• Fertility is usually high.
• Examples:
• Wheat (Triticum aestivum – hexaploid)
• Cotton (Gossypium)
• Tobacco (Nicotiana)


4. Polyploidy and Meiosis
• Polyploidy affects chromosome behavior during meiosis.
• In autopolyploids:
• Multivalent formation occurs
• Unequal chromosome segregation
• Reduced fertility
• In allopolyploids:
• Bivalent formation
• Regular meiosis
• Stable inheritance


5. Role of Polyploidy in Plant Evolution
• Polyploidy increases genetic variation.
• It helps plants adapt to changing environmental conditions.
• Polyploid plants often show:
• Hybrid vigor (heterosis)
• Increased resistance to diseases
• Tolerance to stress conditions
• Many flowering plants originated through polyploidy.


6. Importance of Polyploidy in Plant Breeding
• Polyploidy is widely used in crop improvement programs.
• Advantages include:
• Increased yield
• Larger fruits and flowers
• Improved quality
• Development of seedless fruits:
• Triploid watermelon (3n)
• Polyploid crops show better economic value.


7. Cytogenetic Significance
• Polyploidy is a key concept in cytogenetics.
• Helps in understanding:
• Chromosome pairing
• Numerical chromosomal changes
• Genome evolution
• Useful for genetic studies and breeding strategies.

8. Conclusion
• Polyploidy is an important numerical chromosomal change.
• It has major applications in plant evolution and agriculture.
• Understanding polyploidy links cytogenetics with practical plant breeding.
• It is a crucial topic for B.Sc. Botany students from both exam and research perspectives.

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