18 public questions tagged with this topic.
Recombinase facilitates crossing over during the pachytene stage of prophase I in meiosis. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Morphology and Anatomy of Flowering Plants, Topic: Plant structure and tissue systems.
During Prophase I, homologous chromosomes undergo crossing over, increasing genetic diversity. This follows from NCERT principle where relation explains outcome clearly for students.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Biology - Botany portion covering relevant concept, Topic: Plant structure, physiology and applications.
Crossing over occurs during prophase I of meiosis, allowing genetic recombination between homologous chromosomes. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Morphology and Anatomy of Flowering Plants, Topic: Plant structure and tissue systems.
Chiasmata become cytologically visible during diplotene and diakinesis after synaptonemal complex disassembly, appearing as cross-shaped connections between homologs under microscope. They represent late consequence of crossover recombination established chemically in pachytene between non-sister chromatids, where exchange of DNA segments creates physical interlock. Cohesion between sister chromatids distal to crossover site mediated by cohesin Rec8 maintains association, converting molecular exchange into durable tether linking homologs. This tether provides resistance to spindle pulling forces exerted on bioriented bivalents at metaphase I, generating tension that satisfies spindle assembly checkpoint and stabilizes correct attachment via Aurora B mediated error correction. As separase cleaves arm cohesin during anaphase I, chiasmata dissolve, permitting homolog separation toward opposite poles. Thus functions are twofold: genetic consequence facilitating allele shuffling underlying diversity, and mechanical function ensuring accurate segregation. Absence leads to achiasmate chromosomes that segregate randomly, increasing aneuploidy risk. This circuitry is highly conserved across eukaryotes, integrating growth factor signals, DNA damage surveillance, and developmental cues, and its disruption frequently underlies oncogenesis, providing targets for checkpoint inhibitors and cancer therapeutics.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 21: Chiasmata and Homolog Cohesion.
Pachytene represents longest stable meiotic prophase stage where fully synapsed bivalents thicken and crossing over implemented. Molecular hallmark is homology-directed repair of programmed double-strand breaks introduced by Spo11 topoisomerase-like transesterase in leptotene that generates 3 prime single-strand overhangs via MRE11-mediated resection. Overhangs invade homologous duplex mediated by meiosis-specific recombinases DMC1 and RAD51, forming D-loop intermediates. Decision between non-crossover and crossover fate controlled by ZMM proteins MSH4-MSH5 heterodimer stabilizing joint molecules and MLH1-MLH3 heterodimer functioning as resolvase cleaving Holliday junctions as crossover. At least one obligate crossover per homolog pair ensures physical connection via chiasma required for correct biorientation at metaphase I. Pachytene therefore concentrates recombination machinery within synaptonemal complex central region. Defects preventing crossover formation cause achiasmate chromosomes, trigger aneuploidy, and underlie human trisomy risk increasing with maternal age. This circuitry is highly conserved across eukaryotes, integrating growth factor signals, DNA damage surveillance, and developmental cues, and its disruption frequently underlies oncogenesis, providing targets for checkpoint inhibitors and cancer therapeutics.
Ref: Hunter, Cold Spring Harb Perspect Biol 2015, Meiotic Recombination in Pachytene. Alberts 7th ed., Chapter 21.
Crossing over occurs during meiosis and allows genetic recombination between homologous chromosomes.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Search for Genetic Material and RNA World
Crossing over during meiosis increases genetic diversity by exchanging genetic material between homologous chromosomes.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Monohybrid Dihybrid and Test Cross
Crossing over during meiosis exchanges genetic material between homologous chromosomes, increasing genetic diversity.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Monohybrid Dihybrid and Test Cross
Meiosis introduces genetic variation through crossing over during prophase I and independent assortment during metaphase I.
Ref: NCERT Class 11 Biology Chapter 10: Cell Cycle and Cell Division Meiosis - Meiosis II and Significance - Genetic Variability
Crossing over occurs during pachytene of prophase I, not in metaphase II.
Ref: NCERT Class 11 Biology Chapter 10: Cell Cycle and Cell Division Meiosis - Meiosis I - Leptotene Zygotene Pachytene Diplotene Diakinesis
Crossing over occurs during pachytene of prophase I, not in metaphase II.
Ref: NCERT Class 11 Biology Chapter 10: Cell Cycle and Cell Division Meiosis - Meiosis I - Leptotene Zygotene Pachytene Diplotene Diakinesis
During pachytene, homologous chromosomes exchange genetic material through crossing over.
Ref: NCERT Class 11 Biology Chapter 10: Cell Cycle and Cell Division Meiosis - Meiosis I - Leptotene Zygotene Pachytene Diplotene Diakinesis
