We are separating IDH isozymes with starch gel electrophoresis using a pH 6.5 L-histidine, citric acid buffer system. Genetic analyses of the variants observed indicate that two loci are involved in the expression of the IDH bands. We have identified four alleles at each locus. Heterodimers are formed between allelic isozymes at each locus and between nonallelic isozymes for the two loci.

Analyses of data from F2 populations suggest that the two loci segregate independently:
 

	Idh1
Idh2	A4/A4			A4/A6			A6/A6			Total
B4/B4	(4.3)a	3	[3.5]b	(7.5)	8	[7.0]	(3.2)	4	[3.5]	15	[14]
B4/B6	(7.4)	10	[7.0]	(13.0)	12	[14.0]	(5.6)	4	[7.0]	26	[28]
B6/B6	(4.3)	3	[3.5]	(7.5)	8	[ 7.0]	(3.2)	4	[3.5]	15	[14]
Total		16	[14]		28	[28]		12	[14]	56

c^2₄ (independence) = 2.633 0.50 < P < 0.75

c^2₈ (4:2:2:2:2:1:1:1:1) = 3.429 0.90 < P < 0.95

^aExpected values, based upon independence, shown in parentheses.

^bExpected values, based upon 4:2:2:2:2:1:1:1:1 segregation, shown in brackets.

Linkage data indicate that Idh2 is tightly linked (less than 5% recombination) to Mdh2 on chromosome 6. Preliminary data suggest that Idh1 is about 20 map units from Mdh1 which has been located on chromosome 8 (see K. Newton elsewhere in the Newsletter).

C. W. Stuber and M. M. Goodman

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