Transmission ratio distortion

--Doug Mead, Mike Flaherty and Ed Weck

Preferential inheritance of one parental allele (hereafter, TRD, transmission ratio distortion) has been observed in interspecific crosses of mouse (see Biddle, Genome 29:389, 1987), tomato (Kinzer, et al. TAG 79:489, 1990), and other plant species (see Zamir et al., Bot.Gaz. 147:355, 1986). TRD has also been observed in maize crosses associated with Ga on chromosome 4S (Jones and Mangelsdorf, Anatomical Record 31:351, 1925). We report TRD on chromosome 4L in a cross of two elite inbred lines.

During the analysis of an F2 population created from two inbred lines, six of 108 loci gave ratios deviating from Mendelian expectations (Chi squared >5.99, 95% confidence level). Of particular interest was the long arm of chromosome 4, see Figure 1, where four of the six non-randomly segregating probes were located (Two of those probes exceeded Mendelian segregation expectations at the 99.5% confidence level; Chi squared > 10.60). In the other two cases (UMC67, 1L, Chi squared=8.70 and BNL10.17, 10S Chi squared=6.10), only a single probe per chromosome with a deviant Chi squared value was observed. These results are similar to those obtained by Kinzer et al. in tomato.

TRD in other plant species has been attributed to selection during one or more of the following phases of the plant's life cycle (Zamir et al.): 1) between meiosis and the formation of the mature gametophytes; 2) from pollination until fertilization of the embryo; 3) during seed development; and 4) during seed germination and plant growth. We have no indication of where in the maize life cycle TRD occurs in this F2 cross. Additional populations with these inbred parents will be analyzed for evidence of TRD on chromosome 4L.

Figure 1.  Transmission Ratio Distortion in an F2 Population.


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