In general, the placement of duplicate genes to chromosomes has not been accomplished. This note outlines a procedure for locating such genes to chromosome arms by using the B-A translocation series. For example, the irregular kernel arrangement in Country Gentleman sweet corn results from the development of both the upper and lower florets of most pistillate spikelets (W. A. Huelsen and M. C. Gillis, Ill. Agric. Exp. Stn. Bull., Vol. 320, 1929 [ed. note: authorship attributed to W. A. Hudson or W. A. Huelson in past publications is inaccurate]). The symbols given to these duplicate genes are pi1 and pi2. The initial step in the procedure involves pollinating Country Gentleman by the basic series of B-A translocations. During the next season, hypoploids for each arm are selected and pollinated by or crossed onto Country Gentleman. In the third season, seed of each backcross progeny is planted out and open pollinated ears are harvested at maturity. Only in those families where the appropriate B-A translocation has uncovered one of the two genes will there be a 1:1 segregation of normal vs. irregular row arrangement. Families involving translocations that fail to uncover either of the two genes will segregate the trait in the normal 3:1 ratio.
Some alterations in this technique may be required for other duplicate gene systems, such as those controlling lethal traits. Results from the Country Gentleman crosses by the B-A translocation series will be forthcoming.
Bryan Kindiger and J. B. Beckett
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