When two maize inbred lines are crossed with each other the hybrid offspring
have a significantly higher yield than either of the two parent plants.
Plant breeders have long known the "heterosis effect," but what causes it is
unclear.

Scientists at the University of Bonn led by Prof. Dr. Frank Hochholdinger
from the Institute of Crop Science and Resource Conservation (INRES) at the
University of Bonn have now investigated a number of genetically distinct
hybrids. They studied six different inbred-hybrid combinations. According to
Jutta Baldauf from INRES, they have analyzed which genes were transcribed in
the original plants and which were in the offspring. They showed that the
offspring had many more active genes than the original parents.

Baldauf explains, "On average, we therefore count more active genes in the
offspring." Maize has around 40,000 genes in total, but the scientists put
the genetic gain at 500 to 600 additionally active genes on average. "The
complementation of Single Parent Expression' could be one of the factors why
hybrids perform better than their parents," says Prof. Hochholdinger.

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