Which is NOT a cause of somaclonal variation?
Causes of somaclonal variation encompass genetic epigenetic disruptions triggered by tissue culture environment, but pollination mechanism is unrelated because in vitro regeneration occurs without sexual fertilization. Authentic causes include gene mutations from replication errors under rapid division error prone repair under oxidative stress, chromosome number changes aneuploidy polyploidy due to spindle abnormalities c mitosis endoreduplication induced by culture hormones colchicine like effects, structural rearrangements translocations deletions from DNA strand breaks, activation of dormant transposable elements such as Ac Ds Mu or retrotransposons like Tos17 which excise insert causing insertional mutagenesis and genome shuffling, and epigenetic changes including altered cytosine methylation at CpG islands histone modifications regulating gene expression stability. Prolonged callus phase duration high 2,4-D concentration age of donor tissue and repeated subculture amplify variation frequency. Pollination mechanism describing self cross compatible outcrossing insect wind mediated pollen transfer belongs to sexual reproduction in field influencing seed set heterozygosity, not operating in axenic culture boxes where no pollinators pollen tubes or fertilization events occur, therefore cannot generate somaclonal variation observed among regenerants.
Ref: Kaeppler 2000 somaclonal causes transposons; NCBI causes methylation mutation.