Because Inr2 exhibits dominant inhibition of aleurone color, easily scored on the ear in the presence of appropriate R1 alleles (herein referred to as R1-S, or susceptible alleles), we chose to map inr2 using a set of wx1 marked A-A translocations. Plants homozygous for Inr2 and R1-S were crossed to a series of wx1-marked translocations in a colorless aleurone (r1) background. F1 plants were backcrossed by a homozygous inr2 wx1 R1-S line, and the resulting ears were scored for colorless (Inr) vs. colored (inr) and waxy (wx) vs. starchy (Wx) kernels (Table 1). In crosses involving wx1 y1 T6-9e, some of the backcrosses were made by plants homozygous for inr2, wx1, y1, and R1-S, so three-point linkage data for wx1, y1, and inr2 were obtained (Table 2). All crosses demonstrated linkage of inr2 with wx1, indicating that inr2 is located on chromosome 9. The distance between wx1 and inr2 showed variability (from 7.6 centimorgans to 30.3 centimorgans) depending upon which A-A translocation was used in the linkage cross. This kind of linkage variability is not unusual in crosses involving translocation stocks (E. B. Patterson, 1952. Ph.D. Thesis, California Institute of Technology). Furthermore, the production of viable duplicate-deficient eggs by adjacent disjunction when plants heterozygous for certain translocations are used as females in linkage crosses can also distort linkage data somewhat.
The linkage data obtained from the crosses with T6-9e (breakpoints 6L.18 9L.24) provide sufficient information to fix the location of inr2 on chromosome 9 with respect to wx1. Because y1 is located on the 9-6 chromosome very close to the breakpoint in T6-9e, and the gene order determined from the linkage data is clearly wx1 y1 inr2, inr2 has to be located on 9L distal to the T6-9e 9L breakpoint (9L.24). If we take the T6-9e linkage data for the wx1--inr2 distance (25.2 centimorgans) as a minimum value for the distance between wx1 and inr2, inr2 is located near or distal to bk2 on 9L. Additional tests using B-A translocations and 9L linkage markers will be conducted to confirm and refine the location of inr2 on 9L.
Table 1. Two point linkage data for
wx1 inr2 in crosses involving various A-A translocations.
Testcross: [wx1 T inr2 r1 / Wx1 N Inr2 R1-S] X wx1 N inr2 R1-S.
|Translocation||Wx Inr||wx inr||wx Inr||Wx inr||% recombination wx1--inr2|
|T1-9(5622)||246||182||60||82||24.9 +/- 1.8|
|T1-9(8389)||292||289||47||49||14.1 +/- 1.3|
|T2-9c||215||385||120||69||24.0 +/- 1.5|
|T2-9b||177||131||48||86||30.3 +/- 2.2|
|T2-9d||205||200||34||83||22.4 +/- 1.8|
|T3-9(8447)||204||245||13||24||7.6 +/- 1.2|
|T3-9(8562)||75||74||16||8||13.9 +/- 2.6|
|T4-9(5657)||296||212||63||48||17.9 +/- 1.5|
|T5-9(022-11)||254||250||22||46||11.9 +/- 1.4|
|T5-9a||214||184||59||47||21.0 +/- 1.8|
|T7-9a||250||248||41||78||19.3 +/- 1.6|
|T8-9d||213||194||47||66||21.7 +/- 1.8|
Table 2. Three point linkage data for
wx1 y1 inr2 in crosses involving T6-9e.
Testcross: (wx1 y1 T6-9e inr2 r1 / Wx1 Y1 N Inr2 R1-S) X wx1 y1 N inr2 R1-S.
|0||wx y inr||459|
|Wx Y Inr||497||956|
|1||wx y Inr||125|
|Wx Y inr||99||224|
|2||wx Y Inr||29|
|Wx y inr||24||53|
|1 + 2||wx Y inr||9|
|Wx y Inr||10||19|
Return to the MNL 75 On-Line Index
Return to the Maize Newsletter Index
Return to the Maize Genome Database Page