ESTIMATION OF AVERAGE DOMINANCE OF GENES 495 



Experiment I 



The experimental material is produced from matings among plants of the 

 F2 generation of a cross of two inbred lines. Each plant used as a pollen parent 

 is mated with n seed parents, no seed parent being involved in more than one 

 mating. Thus, if sm pollen parents are used there will be smn seed parents 

 used in smn matings. The progenies of these smn matings comprise the ex- 

 perimental material. All parent plants are chosen from the F2 population at 

 random. 



Pollen parent and seed parent plants will for brevity be referred to in what 

 follows as males and females, respectively. A group of n progenies having the 

 same male parent will be referred to as a male group. 



The field arrangement of the material is based on division of the sm male 

 groups into 5 sets each of which contains mn progenies in m male groups. 

 Each set of progenies comprises the material for a distinct unit of the experi- 

 ment and is planted in a randomized block arrangement having mn entries 

 and r replications. Thus the total field arrangement is composed of s inde- 

 pendent units, each unit being devoted to a different set of progenies. Data 

 on characters of interest are collected on k plants per plot. 



Experiment I! 



This is a modification of Experiment I that can be used when dealing with 

 multi-flowered plants. The foundation stock is again the F2 generation of a 

 cross of inbred lines. In this case, however, a set of mn progenies is produced 

 by making all of the mn possible matings of w. males and n females chosen at 

 random from the F2 population. With annual plants this can be done (and 

 the progenies kept distinct) only if more than one pistillate flower per plant 

 is available. It could not be done, for example, with single-eared corn. 



The field arrangement is as described for Experiment I, the sets arising 

 from the mating plan being maintained intact in the units of the field struc- 

 ture of the experiment. 



Experiment III 



The experimental material is produced from backcross matings of F2 

 plants to the two inbred lines from which the F2 was derived; the F2 plants 

 are used as pollen parents. A set of progenies is made up of the 2n progenies 

 obtained from backcrossing n random F2 plants to each of the parent in- 

 breds. The number of inbred plants used in production of each backcross 

 progeny is important only with respect to insuring sufficient seed. 



The total experimental material consists of s sets of n pairs of progenies. 

 The members of each pair have the same F2 (male) parent but different in- 

 bred parents. The two inbred parents are, of course, the same for all pairs of 

 progenies. 



The field arrangement is analogous to that for Experiments I and II. The 



