2. The phenotypic expression of variegated pericarp in VV/WR plants in which the WR allele was derived from two otherwise comparable classes of VV/WR heterozygotes, namely, light variegated and medium variegated.

It was demonstrated in 1929 by R.A. Emerson (Genetics 14:488‑511) that following self‑pollination of variegated pericarp corn plants heterozygous for colorless pericarp, red cob (VV/WR) the resulting VV/WR offspring regularly show a higher rate of somatic mutation of variegated to red pericarp than the VV/VV offspring. This relation held in spite of the fact that in the latter class of individuals there are present two VV alleles capable of such mutation as against only one in the former class. The conclusion was drawn that WR, or a gene closely linked with it, enhances the mutability of VV in VV/Wr heterozygotes. Furthermore, Emerson reported data which led to the suggestion that the capacity of a given WR (or a closely linked gene) to "stimulate" mutation of variegated to red might be decreased as a result of association with VV in variegated heterozygotes of low grade (i.e., having a low rate of mutation of variegated to red). The present experiment was prompted by this seemingly valid and unaccountable fact.

A part of the same collection of pollen from plant S1937‑10 as referred to in Table 1, above, was placed on the silks of the colorless pericarp, red cob inbred lines W22, W23, W28, W70 and M14. The resulting five F₁ families each comprised light variegated, medium variegated, and red pericarp individuals as a consequence of the previously noted fact that the tassel of S1937‑10 was a chimera. The three sharply distinct classes of F₁ plants were used as the pistillate parents in crosses with individual variegeted plants heterozygous for colorless pericarp, white cob (VV/WW) unrelated to S1937‑10. Series of 10–25 plants within a given F₁ family were pollinated with a single collection of pollen. This gave groups of light variegated and medium variegated outcrossed ears in which the seeds throughout each group had a common male parent. The F₁ red ears so pollinated were not tested further.

Essentially this procedure involved passing the WR alleles originally derived from the five inbred lines through a corresponding series of F₁'s represented in each instance by otherwise closely comparable light variegated and medium variegated plants. The extracted WR alleles were then reassociated in F₂ with variegated pericarp from a different source.

Sixty‑seven such F₂ families were grown in 1950. The variegated pericarp, red cob (VV/WR) ears from them were saved as constituting the sub‑group applicable to the study. It will be evident that the WR alleles carried by these ears were derived from the light and medium variegated F₁ VV/WR plants; the VV genes now paired with the WR's were derived from quite unrelated stocks. These red‑cobbed, variegated F₂ ears were then scored for grade of variegation against a set of standard ears. In addition, the number of mutations to red (covering about 1/5 kernel or more) was counted on the ears in 17 families.

The results showed that in 16 of the 17 paired comparisons which could be made, regard being given both to the origin of the WR allele and common male parentage, the variegated progeny carrying WR genes extracted from light variegated F₁ plants had a definitely lower mean grade of variegation than the VV/WR progeny which had received the WR allele from a medium variegated sib. The respective mean grades were similar in the single remaining comparison. The mean difference in grade throughout was a little less than one class on the arbitrary scale of standards employed. However, the F₂ families corresponding to light variegated F₁'s, on the average, exhibited significantly fewer mutations of variegated to red pericarp per 1000 kernels than the group of families from medium variegated parents.

Our results, when portrayed in this manner are seen to be in clear agreement with Emerson's conclusion relative live to the effect on mutation of VV to RR of WR, or a closely linked gene, extracted from VV/WR heterozygotes of different variegation grades.

The direction in which an explanation of this seemingly anomolous behavior is to be sought took a new turn, however, as one fact, not at first apparont to us, became evident. Re‑examination of the present populations revealed that the distribution of variegated in the F₂ WR segregates actually was discontinuous rather than continuous as we had assumed in procceding to score the ears against the standards. Except in three families in which the distributions appeared to overlap, two definitely recognizable classes of ears only were present in each progeny, light variegated and medium variegated. This observation seemed particularly significant in view of: (1) the similar character of the distribution of VV segregates in backcrosses to WR/WR of the same kinds of F₁ VV/WR plants, as reported in section 1, above, and (2) the fact that in the present instance we were dealing with the WR, rather than the VV, segregates from the light and medium variegated heterozygous parent plants.

Table 2

Distribution in F₂ and mean grade of light and medium variegated
ears among the WR segregates feom [sic] light and medium variegated VV/WR F₁
plants pollinated by VV/WW.

Family number	F1 Parent ear		Variegated progeny				Total ears	Per cent Vlt
	Pedigree	Phenotype	Vlt		Vm
			No.	Mean grade	No.	Mean grade
N‑30	VV/WR‑22	Vlt	35	1.48	23	3.04	58	60.3
N‑36	"	Vm	9	1.44	41	3.12	50	18.0
N‑99	VV/WR‑28	Vlt	13	1.69	19	3.15	34	40.6
N‑102	"	Vm	7	1.71	43	3.04	50	14.0
N‑118	VV/WR‑70	Vlt	18	1.94	14	3.57	32	56.2
N‑121	"	Vm	4	1.75	51	3.02	55	7.3
N‑123	"	Vm	4	1.50	28	3.53	32	12.5

A representative sample of the data relating to the WR segregates from three different F₁ hybrids is presented in table 2. The pollen applied to the W22, W28 and W70 hybrids concerned was collected from three unrelated VV/WW plants. Attention may be called to the following points in the table:

1. Both light variegated and medium‑variegated F₁ parent VV/WR ears outcrossed to VV/WW give families containing WR segregates of these same two classes of variegation.

2. If a common VV/Ww pollen parent is used in matings with light and medium variegated F₁ VV/WR sibs, the light variegated WR offspring from the light variegated ears are similar in variegation grade to the same class of offspring from the medium variegated WR ears. This correspondence holds also for the medium variegated WR offspring of the two kinds of F₁ parents.

3. The proportion of light variegated WR offspring from light variegated F₁ VV/WR ears is much higher than from the medium variegated F₁ ears.

4. Points (2) and (3) above, when considered together, make it evident that the difference in mean grade of variegation in entire progenies of Similarly bred light and medium variegated F₁ ears is due to the difference in proportion of these two classes of offspring.