Soybean has a gene Y11 which is involved in chlorophyll synthesis and is incompletely dominant. This means that the homozygous recessive (y11y11) is yellow and seedling lethal, the homozygous dominant (y11y11) is dark green , and the heterozygote (y11y11) is medium green (a yellowish green) and viable. Because a crossover in the heterozygote would produce a dark green/yellow twin spot on a medium green background, the system has been extensively exploited by Vig and Paddock (1968 and 1969) and Vig (1971, 1972, 1973 and 1975) as a tester system for chemicals suspected of mutagenic activity.
"Research notes: A possible alternate explanation for light green spots on yellow
leaves in the soybean y11y11 test system,"
Soybean Genetics Newsletter: Vol. 5
, Article 6.
Available at: http://lib.dr.iastate.edu/soybeangenetics/vol5/iss1/6