Prophase 1 in meiosis12/22/2023 The actions of ZMM proteins indicate that interfering-crossover sites are selected from potential precursors at an early stage in the meiotic DSB-repair process. Noninterfering crossovers depend on the proteins Mus81 and Mms4. cerevisiae and Arabidopsis proteins are indicated here in parentheses: Rec107 (Mer2), Ski8 (Rec103), Mre2 (Nam8), Sae2 (Com1), Zip4 (Spo22), AtMSH5 (At3G20475), AtMUS81A (At4G30870) and AtMUS81B (At5G39770). cerevisiae proteins but that have not been functionally characterized. Question marks indicate Arabidopsis proteins that are thought to be involved in this process on the basis of their similarity with S. Proteins involved in this process are indicated, together with the stage they are thought to operate at data taken from Ref. Repair results in three different products: interfering crossovers, noninterfering crossovers and noncrossovers. DNA DSBs are formed at leptotene and are processed to form single strands, which then invade a chromatid of the homologous chromosome as a repair template. (b) A model of meiotic recombination pathways in Saccharomyces cerevisiae (yeast) and Arabidopsis thaliana. Then, at diakinesis (the final stage of prophase I), the synaptonemal complex has disappeared, and the further condensation of chromosomes reveals the presence of chiasmata. Next, at pachytene, synapsis is completed, and the synaptonemal complex links the homologs along their whole length. Then, at zygotene, the pairs of homologous chromosomes start to synapse, through formation of the synaptonemal complex. After replication, chromosomes condense into long threads. ![]() (a) The cytological progression of prophase I of meiosis.
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