Crossing over and meiosis

Content
Linkage and Crossing Over in Diploid Organisms (Higher Eukaryotes)
Coupling and repulsion hypothesis
A testcross in maize
Crossing over and meiosis 
Crossing over and chiasma formation
Mechanism of genetic recombination
Crossing over and linkage maps 
Recombination frequencies from a test-cross
Recombination frequencies from F2 data
Interference and coincidence
Linkage maps
Mapping function and poisson distribution
Linkage groups
Chi-square test 
Cytological basis of crossing over
Creighton and McClintock's experiment in corn
Meselson and Weigle's experiment using lambda (λ) phage
Crossing over at four strand stage

Crossing over or recombination actually results from exchange of chromosome segments which is believed to take place during prophase I of meiosis. During prophase I of meiosis, homologous chromosomes are brought together during synapsis at zygotene. Each chromosome also divides longitudinally into two chromatids at this stage. At pachytene, chromatids exchange segments. Homologous centromeres then start separating away from one another (terminalization) and figures of chiasmata are theTesult and not the cause of crossing over.