Arabidopsis thaliana researchers have discovered that "missing" genetic information unexpectedly reappears in later generations yielding offspring with traits identical to the grandparent and not the parent.

Credit: Zina Deretsky, National Science Foundation

Any particular gene in an organism may have alternative variations, as is the case of the "hothead" gene in Arabidopsis. Knowing the genetic variations of the parents allows us to predict the physical description of their prodigy if the genes are passed on according to the basic tenets of Mendelian genetics.

Gregor Mendel's first law, the "Principle of Segregation," asserts that hereditary characteristics are determined by genes appearing in pairs. Usually one of the pair comes from each parent. But this plant fertilizes itself.

So, if a normal hothead gene (abbreviated HTH) is present at all, the plant forms normal blossoms. If the plant has two copies of the mutated hothead gene (abbreviated hth) the plant's blossoms are fused. Therefore, three genetic combinations are possible: HTH/HTH, HTH/hth, and hth/hth. These yield normal, normal, and fused blossoms, respectively.

The observed genetic inheritance of the hothead gene, however, challenges Mendel's first law. The actual outcome of three generations of plant breeding, shown on the right, illustrates the reappearance of normal flowers in the offspring generation. But the parent plant (middle box) seemingly has no HTH copy of the hothead gene to pass on. Therefore, traditional genetic theory may need modification.

Credit: Zina Deretsky, National Science Foundation