Soost, R. K. and J. W. Lesley.
L. Butler has presented data (TGC 8:11-12) indicating that aurea, au, a mutant which appeared in R2 from seed treatment with P^32, is probably in linkage group III or V. Evidence of linkage of au by the Chi square test was strong in both groups but linkage chi square was greater in group III. In his F2 segregations of au and br (group III) not only linkage chi square but the deviations of au and br from the expected 3:1 were significant. In the F2 containing au and hl, the linkage chi square and the deviation of hl^+ to hl from 3:1 is significant but not that of au (chi square = 3.65 d.f.l. P = 0.06).
Tests of linkage between au and y, non-yellow skin color, in group III were made in F2 obtained from selfing an F1 plant from the cross al sp y au^+ x al^+ sp^+ y^+ au. Two F2 families were sown from the same seed source. About 80% to 85% of the seeds germinated. In the first family, 57.45,in the field most of the au plants failed to set fruit but in the second family, 58.032, the au plants were kept in the greenhouse in a cheesecloth cage and three fourths (17/26) of them set fruit.
In the combined F2, including the plants which failed to set fruit, the au+ : au ratio was 118:38; for an expected 3:1, chi square is 0.03, but, counting only those which fruited, there was a slight deficiency of au; chi square was 4.2, P = .04. This was due to the failure of almost half of the au plants to set fruit. The y^+:y ratio in the total F2 was 83:38. Here chi square was a 2.6 and P = 0.1, indicating a non-significant excess of y plants. The y^+:y ratio in the smaller family 57.45 was 20:15 and differs significantly from the expected 3:1 but in the other family, 58.032, the deviation was non-significant.
The F2 combinations were as follows:
Linkage
Family au^+ y^+ au^+ y au y^+ au y chi square
57.45 17 15 3 0 4.3
58.032 46 23 17 0 7.1
Joint 63 38 20 0 11.3
segregation
The linkage chi square in the combined families is significant (P = 0.01) and
indicates fairly close linkage of au and y. The heterogeneity chi squares for
the single genes au and y and for the linkage in the two families were as
follows:
au^+ au y^+ y Linkage DF
Deviation 4.6 2.6 11.3 1
Heterogeneity 1.7 3.5 0.1 1
Total 6.3 6.1 11.4 2
None of the heterogeneity chi squares between the two families is significant.
Actually the combined F2 ratios are nearly those expected with complete
linkage of au and y with chi square = 5 (DF = 2 P = 0.1). These data
certainly support Butler's evidence that au is in linkage group III and is
near the y locus. If au is due to a deficiency, the locus evidently is not
involved since au plants contain this allele. In our experience au^+ au
plants are quite fertile and according to M. M. Lesley (unpublished data)
aurea plants have normal meiosis in the pollen mother cells.