We are modifying a set of forty-five reciprocal translocations and five pericentric inversion stocks so that they will be useful for transposon tagging with the Ac element. The usefulness of these stocks will be enhanced by their detailed genetic and cytogenetic characterization. Presented here are data from nine recombinational mapping experiments to determine the location of several reciprocal translocation breakpoints. The first five experiments tested the location of the breakpoint in chromosome arm 1S and involved the five translocations: T1-3(5597); T1-3(5982); T1-4b; T1-5(6899); and T1-3k. The other four experiments test the location of the breakpoint in chromosome arm 3L and involved the four translocations: T1-3(8995); T1-3k; T1-3(5597); and T1-3(5982).

Plants which are heterozygous for reciprocal translocations show 50% gamete abortion. All plants in this study were scored for semisterile or fully viable pollen. In all mapping experiments the parental translocated chromosome carried dominant alleles at the mapping loci and the parental normal chromosomes carried with them the recessive alleles. Genetic recombination with the breakpoints would bring the recessive traits into coupling with the translocation breakpoint (T). The corresponding locus on the normal chromosome is indicated as N. For these experiments T can be considered as dominant to N. In the tables the loci are shown in the inferred order. The parental (P) class is always presented first. Crossover regions are numbered left to right.

Tables 1 through 5 show the experimental design and the recombination data for the four translocation breakpoints on chromosome arm 1S. The genetic mapping markers were zb4 (zebra4) and P (pericarp color). Homozygous recessive zb4 plants have zebra cross banding on seedling leaves. The P locus conditions both pericarp and cob color and four different alleles were used in these experiments. P-rr produces a red cob and a red pericarp; it is dominant over all other alleles. P-vv displays a variegated red and white pericarp and cob. P-wr conditions a white (actually clear) pericarp and a red cob. P-ww is recessive to all the other P alleles and when homozygous both the pericarp and the cob are white.

Tables 6 through 9 show the data and experimental design for mapping the 3L breakpoints. Homozygous recessive ts4 (tassel seed4) plants have a compact tassel containing both pistillate and staminate florets. Plants which are homozygous lg2 (liguless2) possess reduced ligules and auricles. Kernels which are homozygous for recessive a1 (anthocyaninless1) have colorless aleurones.

Although the order of loci can usually be determined from these data (there was no recombination between T and lg2 in T1-3k), the observed genetic distances between the breakpoints and the adjacent loci are understated. When translocations are heterozygous with normal chromosomes there is generally a reduction in crossing over near the breakpoints.

Table 1. Linkage of T1-3(5597) with zb4 and P. The cytological breakpoints are 1S.77 and 3L.48. The backcross was T Zb4 P-wr/N zb4 P-ww x N zb4 P-ww/N zb4 P-ww.
 

a) P:	T Zb4 P-wr	43	82
	N zb4 P-ww	39
b) CO1:	T zb4 P-ww	7	22
	N Zb4 P-wr	15
c) CO2:	T Zb4 P-ww	3	4
	N zb4 P-wr	1
d) CO1&2:	T zb4 P-wr	0	0
	N Zb4 P-ww	0
		Total=108

% recombination: T-zb4 (b+d)=22 or 20.4%±3.9%; zb4-P (c+d)=4 or 3.7%±1.8%
Conclusion: The breakpoint (T) on 1S is distal to zb4.

 Table 2. Linkage of T1-3(5982) with zb4 and P. The cytological breakpoints are 1S.77 and 3L.66. The backcross was Zb4 T P-rr*/zb4 N P-ww x zb4 N P-ww/zb4 N P-ww.
 

a) P:	Zb4 T P-rr	143	252
	zb4 N P-ww	109
b) CO!:	zb4 T P-ww	26	46
	Zb4 N P-rr	20
c) CO2:	Zb4 T P-ww	11	17
	zb4 N P-rr	6
d) CO1&2:	zb4 T P-rr	2	3
	Zb4 N P-ww	1
		Total=318

*One of four families (N=53) had P-wr as the dominant P allele.
% recombination: T-zb4 (b+d)=49 or 15.4%±2.0%; zb4-P (c+d)=20 or 6.3%±1.4%
Conclusion: The breakpoint (T) on 1S is distal to zb4.

Table 3. Linkage of T1-4b with zb4 and P. The cytological breakpoints are 1S.55 and 4L.83. The backcross was Zb4 P-vv* T/zb4 P-ww N x zb4 P-ww N/zb4 P-ww N.
 

a) P:	Zb4 T P-vv	250	453
	zb4 N P-ww	203
b) CO1:	zb4 T P-ww	2	5
	Zb4 N P-vv	3
c) CO2:	zb4 T P-vv	0	5
	Zb4 N P-ww	5
d) CO1&2:	Zb4 T P-ww	2	3
	zb4 N P-vv	1
		Total=466

*One of four families (N=101) had P-wr as the dominant P allele.
% recombination: zb4-T (b+d)=8 or 1.7%±0.6%; T-P (c+d)=8 or 1.7%±0.6%
Conclusion: The breakpoint (T) on 1S lies between zb4 and P.

 Table 4. Linkage of T1-5(6899) with zb4 and P. The cytological breakpoints are 1S.32 and 5S.20. The backcross was Zb4 P-wr T/zb4 P-ww N x zb4 P-ww N/zb4 P-ww N.
 

a) P:	Zb4 P-wr T	51	83
	zb4 P-ww N	32
b) CO1:	zb4 P-wr T	3	4
	Zb4 P-ww N	1
c) CO2:	zb4 P-ww T	1	3
	Zb4 P-wr N	2
d) CO1&2:	Zb4 P-ww T	0	0
	zb4 P-wr N	0
		Total=90

% recombination: zb4-P (b+d)=4 or 4.4%±2.2%; P-T (c+d)=8 or 3.3%±1.9%
Conclusion: The breakpoint (T) on 1S is proximal to P.

 Table 5. Linkage of T1-3k with zb4 and P. The cytological breakpoints are 1S.17 and 3L.34. The backcross was Zb4 P-wr T/zb4 P-ww N x zb4 P-ww N/zb4 P-ww N.
 

a) P:	Zb4 P-wr T	127	237
	zb4 P-ww N	110
b) CO1:	zb4 P-wr T	5	9
	Zb4 P-ww N	4
c) CO2:	zb4 P-ww T	11	25
	Zb4 P-wr N	14
d) CO1&2:	Zb4 P-ww T	1	2
	zb4 P-wr N	1
		Total=273

% recombination: zb4-P (b+d)=11 or 4.0%±1.2%; P-T (c+d)=27 or 9.9%±1.8%
Conclusion: The breakpoint (T) on 1S is proximal to P.

 Table 6. Linkage of T1-3(8995) with ts4 lg2 and a1. The cytological breakpoints are 1S.49 and 3L.06. The backcross was T Ts4 Lg2 A1/N ts4 lg2 a1 x N ts4 lg2 a1/N ts4 lg2 a1
 

a) P:	T Ts4 Lg2 A1	49	96
	N ts4 lg2 a1	47
b) CO1:	T ts4 lg2 a1	1	3
	N Ts4 Lg2 A1	2
c) CO2:	T Ts4 lg2 a1	16	39
	N ts4 Lg2 A1	23
d) CO3:	T Ts4 Lg2 a1	25	60
	N ts4 lg2 A1	35
e) CO1&2:	T ts4 Lg2 A1	0	0
	N Ts4 lg2 a1	0
f) CO1&3:	T ts4 lg2 A1	1	3
	N Ts4 Lg2 a1	2
g) CO2&3:	T Ts4 lg2 A1	2	4
	N ts4 Lg2 a1	2
h) CO1,2&3:	T ts4 Lg2 a1	0	1
	N Ts4 lg2 A1	1
		Total=206

% recombination: T-ts4 (b+e+f+h)=7 or 3.4%±1.3%; ts4-lg2 (c+e+g+h)=44 or 21.4%±2.9%; lg2-a1 (d+f+g+h)=68 or 33.0%±3.2%
Conclusion: The breakpoint (T) on 3L is proximal to ts4.

 Table 7. Linkage of T1-3k with ts4 lg2 and a1. The cytological breakpoints are 1S.17 and 3L.34. The backcross was Ts4 T Lg2 A1/ts4 N lg2 a1 x ts4 N lg2 a1/ts4 N lg2 a1.
 

a) P:	Ts4 T Lg2 A1	71	148
	ts4 N lg2 a1	77
b) CO1:	ts4 T Lg2 A1	11	30
	Ts4 N lg2 a1	19
c) CO2:	Ts4 T lg2 a1	0	0
	ts4 N Lg2 A1	0
d) CO3:	Ts4 T Lg2 a1	29	46
	ts4 N lg2 A1	17
e) CO1&2:	ts4 T lg2 a1	0	0
	Ts4 N Lg2 A1	0
f) CO1&3:	ts4 T Lg2 a1	6	13
	Ts4 N lg2 A1	7
g) CO2&3:	Ts4 T lg2 A1	0	0
	ts4 N Lg2 a1	0
h) CO1,2&3:	ts4 T lg2 A1	0	0
	Ts4 N Lg2 a1	0
		Total=237

% recombination: ts4-T (b+e+f+h)=43 or 18.1%±2.5%; T-lg2 (c+e+g+h)=0 or 0.0%±0.0%; lg2-a1 (d+f+g+h)=59 or 24.9%±2.8%
Conclusion: The breakpoint (T) on 3L lies between ts4 and lg2.

 Table 8. Linkage of T1-3(5597) with ts4 lg2 and a1. The cytological breakpoints are 1S.77 and 3L.48. The backcross was Ts4 Lg2 T A1/ts4 lg2 N a1 x ts4 lg2 N a1/ts4 lg2 N a1.
 

a) P:	Ts4 Lg2 T A1	59	124
	ts4 lg2 N a1	65
b) CO1:	ts4 Lg2 T A1	14	25
	Ts4 lg2 N a1	11
c) CO2:	ts4 lg2 T A1	0	0
	Ts4 Lg2 N a1	0
d) CO3:	Ts4 Lg2 T a1	25	42
	ts4 lg2 N A1	17
e) CO1&2:	Ts4 lg2 T A1	1	2
	ts4 Lg2 N a1	1
f) CO1&3:	ts4 Lg2 T a1	4	6
	Ts4 lg2 N A1	2
g) CO2&3:	ts4 lg2 T a1	0	1
	Ts4 Lg2 N A1	1
h) CO1,2&3:	Ts4 lg2 T a1	0	0
	ts4 Lg2 N A1	0
		Total=200

% recombination: ts4-lg2 (b+e+f+h)=33 or 16.5%±2.6%; lg2-T (c+e+g+h)=3 or 1.5%±0.9%; T-a1 (d+f+g+h)=49 or 24.5%±3.0%
Conclusion: The breakpoint (T) on 3L lies between lg2 and a1.

 Table 9. Linkage of T1-3(5982) with ts4, lg2 and a1. The cytological breakpoints are 1S.77 and 3L.66. The backcross was Ts4 Lg2 T A1/ts4 lg2 N a1 x ts4 lg2 N a1/ts4 lg2 N a1.
 

a) P:	Ts4 Lg2 T A1	47	97
	ts4 lg2 N a1	50
b) CO1:	ts4 Lg2 T A1	19	49
	Ts4 lg2 N a1	30
c) CO2:	ts4 lg2 T A1	5	11
	Ts4 Lg2 N a1	6
d) CO3:	Ts4 Lg2 T a1	5	11
	ts4 lg2 N A1	6
e) CO1&2:	Ts4 lg2 T A1	1	1
	ts4 Lg2 N a1	0
f) CO1&3:	ts4 Lg2 T a1	5	5
	Ts4 lg2 N A1	0
g) CO2&3:	ts4 lg2 T a1	1	3
	Ts4 Lg2 N A1	2
h) CO1,2&3:	Ts4 lg2 T a1	0	0
	ts4 Lg2 N A1	0
		Total=177

% recombination: ts4-lg2 (b+e+f+h)=55 or 31.1%±3.5%; lg2-T (c+e+g+h)=15 or 8.5%±2.1%; T-a1 (d+f+g+h)=19 or 10.7%±2.3%
Conclusion: The breakpoint (T) on 3L lies between lg2 and a1.

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