Table III

Strain:		Curly		tra2^ts2

	Prediction:	f	m	f	m
Truth:	percentages:
Curly (18°C):	female	66.67	33.33	0.00	0.00
	male	17.78	82.22	0.00	0.00

tra2^ts2 (18°C)	female	0.00	0.00	100	0.00	*
	male	0.00	3.45	10.34	86.21

Table III. Truth contingency table for 18°C controls of tra2^ts2 temperature-shift sex discrimination experiment on Drosophila melanogaster. This table documents a typical control group result of this f2-hybrid cross in which the objective is to sort out the tra2 genetic females (*) in order to assess the sexual phenotype that they are expressing. We demonstrate the effectiveness of using wing landmark discriminant functions in helping accomplish the goal. The truth in this table is represented by the 'apparent' Curly phenotype (tra2 segregants are non-Curly) and Barr-eye-of stone tag on males determines sex of the individuals. Independently, a prediction of sex and Curly phenotype was made using four discriminant functions based on the analysis of the wings' landmark coordinates. The most important result is that when a truth assignment to Curly is made it is invariably correct (i.e. the probability of a false positive is vanishingly small). However sometimes the Curly phenotype is leaky and appears close to the non-Curly wild type (i.e. the probability of a false negative is not zero). Luckily, the Curly phenotype is also very distinctive as recognized by its discriminant function. Occasionally a presumed tra (i.e. by its apparent non-Curly appearance by visual inspection) is predicted to be Curly by the discriminant function. These wings (the 3.45% of tra males in row four of the table) are removed from the analysis and assumed to have been Curly visual non-penetrants. This two-level sorting of the experimental strain is relied upon during temperature shift experiments to sort out potential false positive tra-2 segregants. Using this double sorting it is seen that the control group of interest in the above table, tra2^ts2 (18°C) females, behaved perfectly with 100% of the row's individuals being predicted to be tra2 females.

Last update: 97/01/01
J. G. Kunkel