In the parents, the normal gene copy compensates for the bad copy.

However, the child who inherits two defective gene copies cannot produce enough effective enzyme and develops the genetic metabolic disorder.

The mouse model used, had one defective gene copy.

Thus, 60% (three of five) of the gene copies in the male's bacteriome are absent from the rest of the male (Figure 2).

In contrast, a female is equally related to a son as she is to a daughter (each carries half of her gene copies).

As they do so, they add a marker to each gene copy.

Then they pour a solution containing the gene copies over a nylon strip embedded with all the variants of the six genes.

This can be revealed by an accelerated rate of amino-acid change after duplication in one of the gene copies.

In some of Jordan's blood cells, one gene copy has the mother's defect and the other has the father's flaw.

But in other blood cells, the gene copy from his mother is normal - the tiny but devastating defect is gone.