Practice question

Mating type conversion involves copying information from silent donor into broken MAT locus. After HO induced break, resected MAT end invades HML or HMR sharing Z1 and W homology regions forming D-loop. Repair synthesis copies Ya or Yα sequence from donor, then nascent strand dissociates from donor and anneals back to second end of MAT, filling gap without establishing stable double Holliday junction or crossover between chromosome III regions. This synthesis-dependent strand annealing mechanism results in non-crossover gene conversion, preserving donor cassette unchanged while converting recipient MAT sequence, ensuring donor not lost and maintains switching plasticity.