--Brent Buckner and Philip S. Stinard
The white cap locus (Wc) is a dominant gene which conditions white endosperm in a homozygous recessive y1 background or pale yellow endosperm with a white crown in the presence of Y1. The inbred line A188 also carries a dominant gene for white endosperm which exhibits phenotypically similar epistatic interactions with the y1 locus. We have conducted experiments to determine the allelic constitution of A188 for the y1 locus and also to determine if the dominant white gene in A188 is allelic to Wc.
To determine the allelic constitution of inbred line A188 for the y1 locus, we crossed A188 plants to plants that were homozygous for both the Y1 allele and the recessive wildtype wc allele (Y1/Y1, wc/wc). The progeny kernels from this cross were all pale yellow endosperm with a white crown. The plants derived from these seeds were crossed to plants which were homozygous recessive for the y1 and wc alleles (y1/y1, wc/wc). If A188 was homozygous for y1, the progeny kernels of this cross would be expected to segregate in a 1:2:1 ratio for pale yellow with white crown, white, and yellow endosperm. If, on the other hand, A188 was homozygous for Y1, the progeny kernels of this cross would be expected to segregate in a 1:1 ratio for yellow and pale yellow, white-crowned endosperm. The observed phenotypes and total number of kernels of each phenotype are found in Table 1. The chi-square values indicate that the data do not significantly deviate from a 1:2:1 ratio in six of seven crosses. In the seventh cross, the data deviated significantly at the 5% level. The total counts for all seven ears do not significantly deviate from 1:2:1. We conclude from these data that inbred line A188 is homozygous for the recessive y1 allele.
Table 1. Kernel counts for the testcross [A188 x Y1 Y1 wc wc]
x y1 y1 wc wc.
|Ear number||pale yellow- white crown||white||yellow||Chi-square value|
*Chi-square significant at p < 0.05.
To determine if the dominant white gene in A188 is allelic to Wc,
A188 plants were crossed to plants homozygous for Wc and y1
(Wc/Wc, y1/y1; inbred K55, supplied by Dr. Earl Patterson).
The progeny kernels from this cross had white endosperm, which is in support
of our finding that A188 is homozygous for y1. (If A188 was homozygous
for Y1, this cross would have produced kernels with pale yellow,
white-crowned endosperm.) The plants derived from these seeds were reciprocally
crossed to plants homozygous for the Y1 and wc alleles. If
the dominant white gene of A188 is allelic to Wc all of the kernels
produced in this cross are expected to have pale yellow, white-crowned
endosperm. If, on the other hand, the dominant white gene of A188 is not
allelic and is unlinked to Wc, this cross is expected to produce
kernels segregating in a 3:1 ratio for pale yellow, white-crowned to yellow
endosperm. We found that all kernels produced from this cross were pale
yellow with a white crown, therefore, the dominant white gene of inbred
A188 is allelic to Wc.
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