Golden-2 (g2) has a more extreme phenotype than g. The culms and leaf
sheaths are nearly white. The current linkage maps indicate that g2 is
located on chromosome 7, locus unknown. In scoring some F2 families segregating
for this trait (source: Coop. 64-169) and various chromosome 7 markers,
the ease with which multiple gene combinations were recovered suggested
that g2 might not be on this chromosome. A definitive answer was sought
from backcross tests with sizeable populations. The first four lines of
the following table summarize the relevant two point tests from the testcross
g2/o2 v5 ra gl x g2 o2 v5 ra gl (3 families, 1050 total plants). The last
line is from the testcross g2/bd x g2 bd (4 families, 1180 total plants).
There was good homogeneity among the families of each cross for single
gene segregations as well as for independence. The single factor segregations
of g2 and of each of the marker genes did not deviate significantly from
the expected 1:1.
|Tester Mutant||+ +||+ t||g2 +||g2 t||Total||Percent recombination|
None of these deviate significantly from independence. The known map of chromosome 7 is presently 112 crossover units long. Based on chiasma frequency the theoretical length of this chromosome is 123 map units (Rhoades, 1955), therefore the above data adequately test the entire length of this chromosome. It is concluded that g2 does not lie on chromosome 7.
This conclusion is supported by a subsequent test with an A-B translocation. When F1 plants of the constitution g2/o2 v5 ra gl were pollinated by plants carrying TB-7Lb, none of the resulting hypoploid plants were g2.
R. H. Whalen
Return to the MNL 53 On-Line Index
Return to the Maize Newsletter Index
Return to the Maize Genome Database Page