1. Aberrant pericarp-color ratios. - A few years ago I reported a recessive zygotic lethal, zl, with its locus near P in chromosome 1 of maize (Genetics 24: 368-384, 1939). The effect of zl is to prevent, with rare exceptions, homozygosis of genes with which it is closely linked, and thereby to change a 3:1 to a 2:1 F2 ratio when zl is linked with a dominant gene or to prevent the occurrence of one class when linked with a recessive gene. When a plant heterozygous for zl is crossed with one lacking zl, there is, of course, no disturbance of ratios in the resulting progeny. The locus of zl relative to other chromosome-1 genes is
Another case of disturbed pericarp-color ratios has occurred in at least three supposedly unrelated lines, all of which, however, are found to have had one individual plant as a common ancestor a few generations back, namely, a chromosome-1 marker with the genotype P br an gs. This suggests that the disturbance is associated with P rather than with its recessive allele.
Two selfed red-eared plants gave progenies totaling 83 red to 89 white while three other selfed reds gave progenies with normal 3:1 ratios. The former also gave aberrant and the latter normal ratios when used as the pollen parent in crosses with white-eared plants. Fourteen cultures, resulting from white pollinated by heterozygous red, have had a total of 329 plants with red and 1148 with non-red ears. Some of these crosses have involved also T1-3a, the totals being 404 T and 120 non-T. Two cultures involved ms17, P, and T1-3a, from the cross:
|ms + +||/||+ P +||. This 3-point test gave the following results:|
|ms + T|
|18 152||0 6||10 18||0 2|
The percent of recombination is: ms - P = 3.9, P - T 14.6. The recombination value for P - T is less than that indicated by Anderson (News Letter 14 p. 2. 1940). The striking thing, however, is the ratios of dominant to recessive markers, as follows:
+ : ms = 28 : 178
P : + = 36 : 170
+ : T = 42 : 164
From these aberrant ratios it may be inferred that the locus of the disturbing element is to the left of ms17. Whether the disturbing factor is transmitted through the egg is not known. It is transmitted through the pollen. Only a part of the red ears of a culture that shows the aberrant ratio yield such ratios in the following generation.
The nature of the responsible gene, if gene it is, is not known. It is certain, however, that it is not a recessive zygotic lethal and not a complete pollen lethal. So far as now known, it might be a pollen semi-lethal or a gamete factor, but if the latter, it differs in some respects from the Ga gene that disturbs the ratios of the starchy-sugary pair and other characters of chromosome 4.