DOMINANCE OF RECESSIVES
A. Jay Garrison
If dominance is an absolute principle and its relation to recessives is immutable, our subject is an absurd contradiction of terms, but these suppositions are in no respect true. Especially within the zone of variety, dominance is an extremely variable quantity. Genetic factors operate from radiating centers which may be readily shifted by the potency of either side in any given mating, or by a variety of environmental conditions.
Although we then knew nothing of the Mendelian terminology, our attention was first attracted to the principle of dominance in the autumn of 1867, while herding cattle in southern Iowa. In covering portions of four counties we encountered large native orchards of Americana plums. Our previous experience in nursery and horticultural work led us to examine these orchards with absorbing interest. We everywhere found three colors—red, yellow, and mottled or blends. While large groups of the same color were generally found in close proximity, occasionally a specimen of distinct color and variety had maintained its individuality. When examined at blooming time it was found that there was an interim of several days between the time of blooming of the individual tree and the adjacent group.
We have at times been greatly amused at the labored explanations of some scientists who portray nature as adorning herself in a gay attire of many colors and performing all manner of gyrations, à la ballet dancer, in order to attract cross fertilization. Wild trees of the same species often stand in such close proximity that the twigs interlace and yet they never crossbreed by reason of the discrepancy in their time of blooming. For lack of better terms, we denominated the conditions we found in these wild plum orchards as supremacy of color and individual potency. On clay hills and places surrounded by forest trees, the red everywhere predominated, but along ravines where the soil was very rich the yellow came to the front with the largest trees and best fruits. As the tallest grass grew in these places, it was evident that the yellow varieties had been the greatest sufferer from the ravages of prairie fires. This led us to conclude that supremacy of color, or what we now call dominance, was an environmental question. At the return of each spring and autumn these investigations were renewed.
In 1893 we began to cross-breed Americana plums, also to hybridize with Japans, with a view of testing the principles of supremacy of color, individual potency, survival of the fittest, and natural selection by surrounding the seedling with uniformly favorable environment. Before the seedlings fruited the writer removed to Colorado, being very careful that they should accompany him. When the seedlings began to fruit it was evident that climatic environment had wrought a change on all the varieties. High altitude and consequent aridity, low temperature and almost continuous sunshine had decreased all vegetal factors, changed the color of the fruit, and stimulated early bearing, but had not decreased the size, quality or quantity of the fruit.
The variety that first fruited and has since borne the most frequently is a hybrid which displays the greatest amount of response to climatic change. It, with several others, ranks with the best commercial varieties. Its early and continuous bearing, by reason of late blooming and its ability to reproduce itself, easily enables it to hold the place of dominance in Colorado; but in Iowa we do not think it could do this, on account of its diminutive size of tree.
By reason of early blooming the Japan hybrids proved to be of no value on the eastern slope of the Continental Divide. This experience with plum seedlings and hybrids left us in the firm belief that heredity and environment are the tout ensemble of plant breeding.
Soon after removing to Colorado, we began to experiment with corn with a view of producing an acclimatized variety of sugar corn. A search for a suitable base was rewarded by finding a small semi-dent variety which for a generation had matured at an altitude approaching 8,000 feet. With open breeding, this was crossed with White Cob Cory. The result was phenomenal. The length of ear over each parent was increased from 35 to 50 per cent. The acclimatized parent dominated all vegetal factors, the root system, the height of the stalk, distance of the first ear from the ground, etc. Several specimens showed a combined ear length of from 35 to 47 per cent of the entire length of the stalk. A 55-inch stalk produced a 23-inch ear length and a 50-inch stalk one 13-inch ear. This sugar corn has been crossbred with other varieties and bred back with the original base. The latter method appears to produce the better result. An unlimited number of mutations have appeared. One of these has dark red stalks and blades and the husk folds terminate in very prominent blades which are tipped with spinelike points. Another has a stalk about 3 feet in length and trailing suckers from 3 to 5 feet long terminating in fair sized ears. It goes without saying that the mutation making the greatest progress toward perfect acclimatization will assume the position of dominance. In one or the other parent this may have been a latent or recessive factor receiving great impetus from favorable crossbreeding.
This sugar corn has been planted from promiscuous seed and by the ear to row method. It has been tested under favorable and adverse conditions with all dry land farming forage crops recommended by the experts and has outclassed the entire list. Both by irrigation and dry land farming corn was grown by the prehistorics in Colorado, New Mexico, and Arizona, and its possibilities under all environment found in the United States are the greatest of any cereal in the world. Any desirable kind or color may be produced by an intelligent recognition of the demands of climatic environment.
At about the time that the scientific world came into possession of Mendelian terminology the Rhode Island Red breed of poultry appeared in the West and the writer began to experiment with this breed in an effort to test the principles of heredity and dominance. They were selected as a base because they gave evidence of having been crossbred for many generations.
We began no less a task than that of determining the heritable factors that had entered into the composition of these birds by continued crossbreeding. Hence this germinal analysis by crossbreeding was done in order to determine what we already had, rather than what we expected to get. Our, then new, conceptions of heredity still left us firmly believing that evolution certainly evolutes, but we had become very suspicious that the cat did not always jump in the direction prescribed by the theoretical formula.
For five successive years the results from breeding this breed were fairly uniform. The Red Game male of the original cross made a creditable showing at controlling the color, form, and beauty of the males. The females were strikingly recessive in all respects except merit; in this, they appeared to be conservators of the merit of all crosses that entered into their composition. They also outnumbered the males from 5 to 20 per cent. The sixth year there was an incredible increase in the number of males, many of which were recessive in color. This result was readily traced to a male bird introduced into the flock that season to secure new blood. More than 90 per cent of his progeny were males, not one of which held the dominant color. Thus he not only reversed the dominance of color which had been fairly well established by five years' careful breeding, but from a commercial consideration he violently reversed the law of the survival of the fittest. In two years he would have assumed complete mastery over a flock of sixty-five females and ten males. For his audacity in wrecking our "best laid plains," the insurgent, with all his kith and kin, was speedily banished.
In crossing Barred Rock female with Red male the offspring were all blacks and all females; 50 per cent were pure blacks and the remainder blacks with slightly mottled breasts and necks. Seven of these pullets were mated with a pure black males, supposed to be a Wyandotte-Minorca cross. Two hundred and twenty-five chicks were hatched from this mating at six different hatchings. As was to be expected, these chicks were not as uniformly black from both black parents as the first generation were from a Rock X Red cross. In the second generation there was nothing visible that could be classified as dominance. The potency of the male was no more in evidence than the individuality of the females. The females were more uniform in color, form, and size than the males. It was a marvelous ensemble of heredity. In the first hatch there was one Barred Rock; in the second, one white; in the third, two whites; in the fourth, one pure buff and one white; in the fifth, four whites; in the sixth, all black or near blacks. Rose combs prevailed in the first two hatches, singles in the last two.
Many of the chicks made a showing at having the dominant color characters as they neared full development, but began to recede at the first annual moulting. We had fine black specimens of five different breeds. The whites were Wyandotte-Minorca blends with very dark legs, and the buff was a diminutive Cochin. All that we expected to get in the second and third generations we got in the second.
Atavism was the most striking feature of this experiment. This is true of all second generation hybrids and crossbreds. It is also true that most, if not more, of the genetic phenomena usually classified as evolution is nothing but atavism. Mutations and so-called sports are the most immediate result of the infinite number of possible combinations of Mendelian pairs. In these combinations the pairs of an almost infinite number of preceding generations are to be taken into account. When the potency of two or more correlative factors is nearly or quite equal, dominance loses control, resulting in a compromising blend. More than 65 per cent of our second generation chicks were such blends.
To some extent, atavism may prevail in the most exclusive artificial fertilization. We place paper sacks upon the tassel and silk of the corn and mantle our trees to exclude foreign pollen. We pronounce our "mirabile dictus" on the evolutionary changes and hold our ear to the earth to hear the much coveted title, Wizard! This is to laugh, for what we got may have been an ordinary bit of heredity. From the same parents we are obtaining three apparently distinct breeds of chickens. While on the face of the returns they are new breeds, in reality we are only perpetuating the heredity of original crosses.