3. Multiple-gene linkage testers. The nine-gene linkage tester previously described has proved useful in determining the linkage relations of charaetpristics whose inheritance is not clear-cut or perhaps quantitative. A single population of 150 to 200 plants is usually adequate for determining which chromosomes are involved. Linkages or indications of linkage have been found for the distichous ear, secondary pistillate florets, hispid and pilose conditions of the leaf sheath, flexibility of the cob, and susceptibility to aphids and smut. Data are given in table 2.

Table 2. Linkage relations of characters in maize.

Character	Linkage with chromosome number									Total number chromosomes tested
	1	2	3	4	6	7	8	9	10
Distichous spike	-	-	-	-	-	-	-	-	+	1413
Secondary pistillate florets	-	+	-	-	-	-	+	-	-	666
Pilose leaf sheath	-	-	I	-	-	-	-	-	I	864
Hispid leaf sheath	-	+	+	-	-	-	-	-	-	666
Flexible cob	-	-	-	+	-	-	-	-	-	666
Susceptibility to aphids	-	-	-	-	-	-	-	I	-	1359
Susceptibility to smut	-	-	+	+	-	+	+	-	+	24264

+ = Linkage

I = Indication of linkage

- = Independent inheritance

Paul C. Mangelsdorf