Golden rice differs from its parental strain by the addition of three beta-carotene biosynthesis genes.

The activity of each mutant was normalized to the activity of the parental strain assayed at the same time.

In the next stage, Rothenbuhler did a 'backcross' of the hybrids with the hygienic parental strain.

All four showed an expected 1 kb shift compared with the parental strain, Ax4, resulting from the presence of the blasticidin resistance cassette (Fig.

However, if parental strains are maintained by in- frequent cloning this is less likely.

Also, as a result of gene recombination, F1 hybrids are not true-breeding and must be reproduced from the original parental strains.

Many times breeders complain that their strain has lost the de- sired aromatic characteristics of the parental strains.

And, the chromosomes that are lost from an aneuploid nucleus during its reversion to a euploid could be a mixture of those in the parental strain.

When invertase activity from individual mutants was normalized to the activity of the parental strains, a range of relative activities were observed (Figure 8).

In addition to precocious aggregation, BS153 mounds were significantly larger than those of the parental strain.