The following points highlight the four main hypothesis proposed for the mechanism of crossing over. The hypothesis are: 1. The Classical and Neo-Classical Hypotheses 2. Partial Chiasma Type Theory 3. Belling's Hypothesis 4. Copy-Choice Hypothesis. Mechanism of Crossing Over: Hypothesis # 1. The Classical and Neo-Classical Hypotheses: The classical hypothesis of crossing over was proposed by Sax in 1932; it [...]
In this article we will discuss about:- 1. Types of Chromosome Pairing 2. Factors Affecting Chromosome Pairing 3. Significance 4. Molecular Basis. Types of Chromosome Pairing: Chromosome pairing may be divided into three main types, viz., primary pairing, secondary association and non-homologous association, which may be further classified (Fig. 11.1). Primary Pairing: Primary pairing is observed at interphase, mitosis [...]
The following points highlight the fourteen main factors affecting crossing over and chiasma formation. The factors are: 1. Temperature 2. Age 3. Water Content 4. Sex 5. Nutritional Effects 6. Chemicals 7. Radiations 8. Shift in Population 9. Variation within the Organism 10. Chromosome Structure 11. Interference 12. Heterochromatin 13. Centromere 14. Genetic Effects. Crossing Over and Chiasma Formation: Factor [...]