Need for Removal of Selectable Marker Gene
Removal of selectable marker genes from transgenic plants is desirable for the following reasons: (i) Consumer groups have expressed concern about the wide-spread distribution of markers imparting resistance against antibiotics and herbicides, in transgenic foods; this poses theoretical risk of horizontal transfer of the marker genes to gut bacteria. It is argued that the resulting resistant bacterial will then not respond to antibiotics used as medicine. (ii) Crosses between transgenic crops will increase the number of copies of the marker genes in a crop, thus not only increasing the probability of horizontal gene transfer, but also enhancing the likelihood of homology dependent gene silencing, thus limiting the long-term use of transgenic crops. (iii) The presence of a marker gene will not allow transfer of an additional gene using the same marker gene (sometimes described as pyramiding of genes). (iv) The marker gene, like the herbicide resistance gene, may be transferred to weeds, due to long term use of herbicide resistant transgenic crops, thus causing ecological problems.