--Craig Echt

The cross sh4 +/+ pr X sh4 +/sh4 pr was made with one pollen parent onto three ears in the double heterozygote family. The frequencies of the four phenotypic classes of the resulting progeny are listed below.
 

	sh4 Pr	Sh4 pr	Sh4 Pr	sh4 pr
1	157	90	91	1
2	140	79	64	4
3	136	64	86	1
total	433	233	241	6
% total	47.4	25.5	26.4	0.66

The only crossover products that can be scored directly from this type of cross are the double recessives generated in the female parent. (The Chi squared value of the Sh Pr phenotypic class is 1.48 and does not significantly differ from expected.) An estimate of recombination between the sh4 and pr loci of 1.3% is obtained if one assumes an equal number of the reciprocal crossover products (+ +).

Attempts to obtain a recombination value from an F2 or test cross were confounded by the very extreme shrunken phenotype of sh4 in certain lines and in Tucson environments. In severely shriveled kernels red aleurones are indistinguishable from purple ones. In the present cross the sh4 pr kernels were easy enough to score but, nonetheless, the double mutant class may be slightly underrepresented due to misclassification of the pr phenotype.

If anyone has an hcf18, A, C, R or hcf18 pr stock from which they could spare some seed I would like to use it in a three point cross to try to place sh4 and hcf18 on the map with respect to pr.

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