Some of the genes from viruses introduced into plants

Some of the genes from viruses introduced into plants in fully functional form often exhibit Mendelian inheritance because

1. the genes are stably integrated in chromosomes
2. the genes are stably maintained in vectors
3. the genes are co-expressed with chromosomal genes
4. the genes are not interrupted by introns

Mendelian inheritance is observed as the viral genes have been stably integrated and thus expresses itself.