The original description of a3 in 1934 by E. W. Lindstrom (MNL 8:10)
identifies "a new recessive anthocyan gene" with data indicating 22% recombination
with golden and 40% with R. Further description apparently is not in the
literature, but the a3 stock supplied from the Stock Center is described
as a recessive intense plant color. C. R. Burnham and R. V. Kowles (MNL
43:113) found no satisfactory evidence of linkage of a3 with R, sr2, or
g. The recessive factor is uncovered by TB-3La (MNL 47:147). The data below
indicate that a3 is a recessive gene whose expression requires an intermediate-level
(barred) B allele. The barred allele in these experiments is B-a3, one
of the low-intensity alleles at this locus (MNL 51:61); since this allele
has been extracted from the a3 stocks, by intercrossing and selfing, as
a homozygous strain that is only barred (i.e., not intense), the intense
a3 expression is controlled by an additional gene. Presumably the additional
requirement is the recessive factor on 3L which, when hemizygous in the
presence of B-a3, intensifies the plant color. F2 progenies from B-a3/b,
a3/+ (F1 plants were barred):
|R constitution, seed color||Barred||Intense*||Green|
|R-g/r-r, colored class||50||25||22|
|R-g/r-g, colored class||40||8||18|
|Expected for 9:3:4||243||81||108|
F2 progenies from B-a3/B, a3/+ (F1 plants were purple):
|R constitution, seed color||Purple||Intense*||Barred|
|R-g/r-g, colored class||27||2||7|
|Expected for 12:1:3||179.2||14.9||44.8|
*Purple plants with green auricle, somewhat less darkly pigmented than B Pl, with faintly pigmented cobs.
Intense individuals in progenies segregating for green and intense (as in the first of the above F2 progenies) have always given barred progeny from crosses with A3 b, demonstrating that intense plants must be a3 B-a3 (i.e., never a3 b). Similarly r-r, R-g and (in a few tests) R-r do not appear to duplicate the effect of B-a3, since intense individuals in segregating progenies have always given barred progeny in the same test cross (i.e., they were never a3 b r-r, for example).
The above observations demonstrate that a3 is a recessive intensifier of the plant color conferred by B-a3 (and presumably other B alleles). Chromosome 3 linkage tests are in preparation.
E. H. Coe, Jr.
Return to the MNL 53 On-Line Index
Return to the Maize Newsletter Index
Return to the Maize Genome Database Page