F2 data (News Letter, March 23, 1937) indicated that pb4 is located between Y1 and Pl in chromosome 6

5. F₂ data (News Letter, March 23, 1937) indicated that pb₄ is located between Y₁ and Pl in chromosome 6. Backcross data obtained last summer, however, suggest rather close linkage of Y₁ and pb_x.

Backcross data:

Genes	Phase	XY	Xy	xY	xy	Total	% Recombination
Y₁ Pb_x	CB	187	2	-	139	328	0.6

Three-point test:

F₁ genotype	0	1	2	1, 2	Total
Y₁ + Pl	170 132	- 2	47 35	1 1	388
+ pbx +	302	2	82	2
		0.5%	21.1%	0.5%

Whether pb_x is located to the right or to the left of Y₁ can not be decided from these data. The white and yellow patches on plants obtained from backcrosses are considerably larger than those found on piebald plants from the F₂, and are found not only on the leaves but also on the husks. This is attributed to the effect of modifiers rather than to environment.

G. A. Lebedeff