--Teresa J. Chan, John E. Fowler, and Michael Freeling

Liguleless-3 is a dominant mutation that alters the ligular region of maize. Lg3 has been genetically mapped near the centromere of chromosome 3. However, its location on a particular arm has not yet been determined. Our intention is to map Lg3 more accurately with respect to RFLP markers and eventually to use molecular probes to locate it on a chromosome arm.

The progeny analyzed were from an outcross of a Lg3 heterozygote (linked to RFLP alleles designated here as "A") in a Mo17 background (linked to RFLP alleles designated here as "M"). DNA was extracted from individual plants using a miniprep method and cleaved using EcoRI. Southern Blot analysis of these samples using RFLP probes in the vicinity of the centromere of chromosome 3 was used to obtain the data presented in the following tables.

Table 1. Recombinant classes and number of progeny. Loci UMC92-BNL8.35-UMC10-Lg3-NPI219.
 

Progeny Type	# progeny
Parental (non-recombinant):
A-A-A-Lg3-A	9
M-M-M-+-M	3
Single Recombination Classes:
M-A-A-Lg3-A	1
A-M-M-+-M	0
M-M-A-Lg3-A	2
A-A-M-+-M	1
M-M-M-Lg3-A	0
A-A-A-+-M	0
M-M-M-+-A	1
A-A-A-Lg3-M	0
Double Recombination Classes Obtained:
A-M-M-+-A	1
A-M-M-Lg3-A	1

Table 2. Additional plants assayed for recombination between loci.
 

Interval	# recombinants	# non-recombinants
BNL8.35-UMC10	2	21
UMC10-Lg3	0	51
Lg3-NPI219	0	4

The data presented above support the order of loci and map distances on chromosome 3 shown below. This order is different from that shown on the most recent RFLP map (Helentjaris, T lab, personal communication), however, it provides the fewest number of double recombinant progeny.
 

No. Recomb./No. Assayed:
                                                       3/19           4/40          1/70            2/23

Figure 1. Genetic map predicted from data (with distances in cM).

The presence of two double-recombinant progeny is surprising, as interference would be expected to suppress these double recombinations. The high frequency of double recombination events may reflect the small sample size. However, the data could also be explained by negative interference influenced by the presence of the centromere. If this is the case, then we cannot assume that the map with the fewest number of double recombination events is necessarily correct. Further analysis of more individuals in this population as well as using plants aneuploid for the entire arm of 3S or 3L will hopefully resolve this question.

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