Biology Reference
In-Depth Information
6.
Hybridization and
Transgenic Organisms
“Organisms with novel combinations of traits are more likely to play novel
ecological roles, on average, than are organisms produced by recombining
genetic information existing within a single evolutionary lineage.”
—T
IEDJE ET AL
. 1989
“Genes do not belong to an organism, they are at best part of a family
of genes that may be very widespread.”
—B
ERINGER
2000
Crop sorghum (
Sorghum bicolor
) is one of the world's most important grain
crops, both in developed areas such as North America and in underdevel-
oped Africa, its native region. Many varieties, all annual and diploid in
chromosome number, are under cultivation. Johnsongrass (
Sorghum
halepense
) is a perennial, usually tetraploid, grass native to the Mediter-
ranean region. Reproducing both by seed and vegetative means, it is one
of the world's most troublesome weeds, especially of grain crops. John-
songrass is now sympatric with crop sorghum in most areas of cultivation.
Although both grasses tend to be self-pollinating, significant outcrossing
occurs, and many Johnsongrass populations in the United States have
experienced genetic introgression from cultivated sorghums.
Arriola and Ellstrand (1996) conducted experiments at two field sta-
tions in California in which Johnsongrass was planted at distances of
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