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#recombination

17 public questions tagged with this topic.

p-n Junction, Depletion Region and Diode Characteristics

The recombination process in a semiconductor:

**Depletion region** also called space-charge region, thickness typically 0.5 μm, contains no mobile carriers, only fixed ions, negative on p-side, positive on n-side, diffusion current due to concentration gradient, drift current due to field, equilibrium when J_drift + J_diff =0, voltage drop mainly across depletion region. Recombination occurs when a free electron collides with a hole, annihilating both and releasing energy, balancing the generation rate at equilibrium. Substituting values gives Reduces free carriers, which matches expected behaviour for this semiconductor device configurat

Ref: NCERT > Physics Book > Electronic Devices > p-n Junction, Depletion Region and Diode Characteristics

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BOTANY

Which of the following is an incorrect statement about recombination?

Recombination occurs between homologous chromosomes during meiosis, not between non-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.

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Linkage Mapping and Tetrad analysis

Tetrad analysis is mainly useful for genetic mapping in

Tetrad analysis depends crucially on physical containment four meiotic products together within common ascus sac, allowing all chromosomes single meiosis scored simultaneously. In haploid fungi like Neurospora and Saccharomyces ascus wall retains spores after meiosis, facilitating orderly recovery and accurate genotyping via micromanipulation dissection. Diploid plants and mammals disperse meiotic products immediately after formation, so tetrads uncollectible and genetically lost. Haploidy simplifies phenotype as genotype directly observable without dominance masking heterozygous effects. Smal

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 5: Tetrad Analysis Model Haploid Fungi

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Linkage and Mapping

Interference is calculated as

Interference concept quantifies how one chiasma formation influences probability another nearby during synaptonemal complex formation. After measuring coefficient coincidence C = observed DCO / expected DCO, interference I = 1 - C converts coincidence into suppression metric ranging zero to one. C values near one produce I near zero meaning no interference, crossovers random and independent. C near zero produces I near one complete suppression where second exchange prevented. Negative interference where I negative indicates excess double crossovers occasionally seen near chromosome ends or in

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 4: Interference Formula 1 minus Coincidence

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Linkage and Mapping

Double crossovers are identified as

Double crossover requires two separate exchange events within short region between three genes. Probability product of two single crossover probabilities makes event relatively uncommon, further suppressed by positive interference that inhibits nearby second exchanges via chromosome axis signaling. Consequently progeny formed by double recombination represent smallest numeric class among testcross offspring, whereas parental nonrecombinant class most frequent and single crossovers intermediate frequency. Recognizing least frequent class as double crossover is key step in mapping because it ide

Ref: Klug et al., Concepts of Genetics, 12th ed., Chapter 5: Least Frequent Class Represents Double Crossovers

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Linkage and Mapping

Genes separated by ≥50 cM show

Genes separated by fifty centimorgans or more experience frequent crossover events along interval including single and double exchanges that randomise chromatid combinations so parental and recombinant gametes appear equally frequent indistinguishable from independent assortment. Genetic map distance measured in centimorgans equals one percent recombination over short intervals but beyond fifty becomes non-additive without mapping function correction like Haldane or Kosambi. Hence genetically distant loci behave as unlinked even though physically on same chromosome showing fifty percent recomb

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 5: Large Map Distances Mimic Independent Assortment

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Linkage and Mapping

Genes showing independent assortment are either

Independent assortment arises either from location on different chromosomes where segregation of homologues randomly shuffles combinations during meiosis, or from placement very far apart on same chromosome where multiple crossovers per meiosis randomise allele associations to fifty percent recombination approximating unlinked behaviour. Closely linked loci show rare recombinants, intermediate distances produce proportional recombination frequencies, while extremely distant loci behave as unlinked despite physical connection on same DNA fibre due to map saturation and interference. Therefore u

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 5: Conditions Producing Independent Assortment Patterns

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Recombination

Chi site sequence in E. coli is

Physical mapping of Chi activity identified consensus octamer as recombination stimulator in Escherichia coli and related enteric bacteria. Sequence 5'-GCTGGTGG-3' is statistically overrepresented in E. coli genome particularly on leading strand core orientation consistent with break repair bias. Orientation-specific hotspot elevates recombination roughly eightfold in its vicinity downstream, but only when encountered from defined direction relative to RecBCD entry due to asymmetric recognition. This sequence is absent in unrelated organisms using different Chi; Bacillus AddAB recognizes unrel

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 5: Chi Octamer GCTGGTGG and Recombination Hotspots

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Recombination

λ integrase mediates recombination between

Bacteriophage lambda integration into Escherichia coli chromosome is classic tyrosine recombinase system establishing lysogeny. Integrase Int recognizes attachment sites attP on circular phage genome and attB located within bacterial gal/bio region. Both sites contain common 15 base-pair core O where crossovers occur, flanked by arm-type binding sites for Int, IHF, and auxiliary factors. Int tetramer catalyzes reciprocal exchange between attP and attB, integrating prophage flanked by hybrid attL and attR sites, reaction favored by Integration Host Factor induced DNA bending and supercoiling in

Ref: Watson et al., Molecular Biology of the Gene, 7th ed., Chapter 12: Lambda attP x attB Integrative Recombination

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