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#genetic recombination

7 public questions tagged with this topic.

Cell Division

Which phase of meiosis involves the formation of the synaptonemal complex?

Prophase of meiosis I is extended into five substages to accomplish pairing, synapsis, and recombination unique to germ cells. Leptotene initiates with chromosome condensation into thin threads and formation of axial elements along each chromatid containing cohesin Rec8 and HORMA proteins. Zygotene marks onset of homologous pairing facilitated by telomere bouquet clustering at nuclear envelope driven by cytoskeletal forces and homology search mediated by DMC1 recombinase. Synaptonemal complex assembly begins in zygotene: lateral elements SYCP2 and SYCP3 polymerize along axes, transverse filame

Ref: Page & Hawley, Annu Rev Cell Dev Biol 2004, Meiotic Synapsis. Alberts 7th ed., Chapter 21, Meiosis I Prophase.

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Microbial genetics

In bacteriophage T4, intragenic recombination was studied by

Seymour Benzer studied intragenic recombination within rII locus of bacteriophage T4, demonstrating gene is divisible linear array rather than indivisible bead. Using overlapping deletions of rIIA and rIIB cistrons, he crossed thousands of mutants, scoring wild-type recombinants on restrictive K12(lambda) host unable to support rII mutant growth. Recombination frequency between adjacent sites measured subgenic distances, building fine-structure map with resolution down to single base pair. Work introduced terms cistron, muton, recon and proved collinearity of recombination map and coding seque

Ref: Benzer S, PNAS 1955-1961, Fine Structure of rII Region; Griffiths et al., Chapter 9: Intragenic Mapping in T4

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Recombination

Spo11 protein introduces which type of DNA break during meiosis?

Meiotic recombination is initiated intentionally to promote homolog pairing and crossovers. Spo11, conserved protein related to archaeal Topoisomerase VI catalytic subunit Top6A, performs controlled cleavage of both strands of single duplex simultaneously, generating double-strand break with covalent phosphotyrosyl links at 5' ends. Unlike single-strand nicks created during replication or base excision repair, these DSBs are highly recombinogenic and activate downstream MRX resection. Absence of Spo11 leads to failure of synapsis and infertility, highlighting essence of programmed DSBs, not sp

Ref: Watson et al., Molecular Biology of the Gene, 7th ed., Chapter 12: Spo11-Mediated Double-Strand Breaks in Meiosis

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Recombination

Heteroduplex DNA is formed during

Heteroduplex DNA consists of strands originating from two different parental duplexes paired together. It forms when the Rad51-ssDNA presynaptic filament invades homologous duplex, opening the donor and annealing its complementary strand to the invading strand. This creates a D-loop structure where one donor strand is displaced. Branch migration can extend the heteroduplex region bidirectionally. If donor and recipient sequences differ at single nucleotides, mismatch in heteroduplex triggers mismatch repair, leading to gene conversion. Formation is central to recombination and mating-type swit

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: Homologous Recombination and Heteroduplex Formation

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Recombination

Genetic recombination mainly occurs during which meiotic stage in eukaryotes?

Eukaryotic meiotic recombination visible as chiasmata formation occurs during prophase I after homologous chromosomes synapse. Substage leptotene condenses chromosomes, zygotene initiates synaptonemal complex assembly pairing homologs, pachytene maintains full synapsis allowing recombination nodules to mature. Spo11 introduces programmed double-strand breaks early, resection produces single-stranded overhangs that invade homologous duplex via RAD51 and DMC1 recombinases during pachytene. Resolution of double Holliday junctions at this stage produces reciprocal crossovers essential for accurate

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 15: Pachytene Stage of Meiotic Recombination

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