Larry,
Darlington (1958) discussed several types of sterility. One of these he called “segregational sterility”, which would fit with the linkages you discussed.
The other kind of individual sterility, and the one which we are in a position to analyse most exhaustively, is due to a lack of uniformity in the products of segregation. This lack of uniformity we may describe as due to the formation by a zygote of gametes genetically different from those which gave rise to it. But what is more to the point is that it depends on the zygote having arisen from the fusion of genetically differing gametes; that is to its being a hybrid, and a hybrid which undergoes crossing-over and segregation at meiosis so as to produce new combinations of genes in a gametic set of chromosomes.
The failure of fertility that we get from these recombinations expected at meiosis in hybrids we may describe as > segregational sterility. > We may consider it in relation to the three kinds of hybrids in which it occurs, gene hybrids, structural hybrids and numerical hybrids, using at the same time the special behavior of tetraploids of hybrid and non-hybrid origin as a test of our conclusions. Darlington: Sterility (1958)
Cook (1909) reported examples of parental traits in cotton that generally hang together in hybrid progeny.
RELATION OF COHERENCE OF CHARACTERS TO INTENSIFICATION
In hybrids between different types of cotton there is a distinct and very general tendency to coordination or coherence of characters. Notwithstanding the fact that there are large numbers of contrasted differences between the parental types, the hybrids sometimes show only the characters of one parent, by a consistent suppression of all the diverging tendencies derived from the other parent. Such plants are likely to be somewhat peculiar in comparison with pure-bred individuals of the type they resemble, but without showing any definite departure beyond the range of variation of the parent type. There appears to be a rather definite gap between these hybrids that resemble one parent exclusively and those that show characteristics of both parents. No cases were found where one character of one parent was definitely expressed in a plant otherwise having an exclusive resemblance to the other parent. If an Egyptian-like plant shows one obvious Upland character other Upland characters are always found very definitely indicated, if not fully expressed.
The production of high-grade lint by the hybrids appears to be definitely related to this coherence of characters. Hybrids which resemble only one parent have also the lint character appropriate to that parent. Special excellence of lint and high fertility have been found only in plants that show their hybridity by the definite expression of characters of both parents. In addition to this general tendency for the characters of the same parent to appear together there is a more particular tendency for corresponding or closely associated characters to preserve their coherence. Thus hybrids with pale flowers also have the flowers of the open, cuplike, Upland form instead of the more narrowly tubular form of the Egyptian flower. Incongruities, such as flowers of Upland shape with the darker Egyptian color, are rare and have been found thus far only on plants which are nearly sterile or otherwise definitely degenerate.
Though the experiments have not been carried far enough to afford conclusive evidence, it appears that the tendency of the Egyptian characters to gain exclusive expression in members of the first and second generations gives place in the later generations to an opposite tendency toward the exclusive expression of Kekchi or Upland characters. This increasing potency of the Upland characters in the later generations may be looked upon as the cause of deterioration of the lint, since it puts to an end the condition of mixed expression of characters under which the intensification appears. Cook: Suppressed and Intensified Characters in Cotton Hybrids
The same problem annoyed those who sought a perennial wheat. It seemed easy enough, to anyone who drank the neo-Mendelist Kool-Aid, but was more difficult in practice. One problem, it seems to me, is that plants must “decide” whether to put aside resources for their old age (perennialism), or invest it all in their progeny (annualism). Any compromise is bound to weaken both options, to some degree.
We face a similar paradox with our roses. Some folks expect a rose bush to start blooming with the crocuses, and continue until the last chrysanthemum fades. But the same folks want the bush to be disease proof and immune to Summer’s heat and Winter’s cold.
Cook was 100 years ahead of his time in some ways. I wrote in the RHA newsletter several years ago about a then new technique, now widely used, of sequencing RNA from various tissues to determine which parent’s genes are being expressed. A group at Iowa ( I think) looked at a hybrid cotton, a single clone since it was sterile, and checked how genes of two parents were expressed. One gave the genetic contribution for early growth, and \the other for flowers as I recall. anyway it was a perfect example of how different teams of genes pull together. the point is, Mendelian inheritance may be mostly a theoretical construct which was useful in its time, but has been largely superceded. It is hard to get “proper ratios” except by careful selection of traits, even in a model organism.
Larry,
Cook was active (really active) before Mendelists and neo-Mendelists (mostly Eugenicists) took over. He had extensive PRACTICAL experience that frequently contradicted the THEORETICAL calculations of the academics. He knew cotton. He knew coffee. He was a member of the expedition to Machu Pichu, where he determined that the massive stone works were agricultural terraces rather than fortifications. He was also the first modern person to recognize that even the valley floors were terraced. He recognized centers of diversity long before Vavilov tried to take credit, but acknowledged that others came to the idea before he did. His views on evolution were far more advanced than Darwin’s: in particular, he noted that the differences between species frequently exceed by far any plausible utility of those differences.
Why didn’t anyone else notice that coconuts survive only where cultivated? Or that the closest relatives of the coconut are native to Mexican deserts? And along these lines he argued persuasively for an American origin to certain agricultural traditions that spread around the world long before Columbus, and also before the Scandinavians.
He recognized that the growth of plants can be greatly altered by changes in the total quantity of light they receive in a day. That is, a Guatemalan cotton that is bushy and productive in its homeland can become a nearly sterile “tree” form when moved to Texas. And he saw that the giant Cuzco corn is very productive, and does not grow particularly tall in the high Andes. He concluded that the higher summer temperatures of most of North America were responsible for this corn growing excessively tall, and bearing little.
Larry,
The early Mendelists and neo-Mendelists were mostly obsessed with visible “unit characters”. Physiological traits, whether unitary or quantitative, must have an influence on survival and competition. This applies to competition among pollen tubes, as well as differential survival of seedlings. For instance, white-flowered peas also lack anthocyanin pigments and tannins in the seeds. These substances contribute to the structural stability of seeds. Thus, seeds that would give rise to white-flowered plants are more likely to rupture and rot when they imbibe water too rapidly. And the growth rate of pollen tubes can be influenced by temperature. Consider a hybrid of a night-flowering plant and a day-blooming relative. In addition to segregation and reassortment of obvious characters (character and shape of the flowers), we should expect segregation of temperature preference for the growth of pollen tubes. In this case, the ratio of segregation could be different if the hybrid flowers are self-pollinated during the heat of the day rather than in the cool of the evening/night. Any linked genes that affect visible characters would be dragged along. Anderson’s study of the Louisiana irises and their hybrids is an example. http://bulbnrose.x10.mx/Heredity/Anderson/Anderson_Introgressive/anderson01.htm
Neo-mendelists also assumed that alternative alleles were the units of selection. One allele should be “better” than others, and more likely to survive. But more recent research shows that linked groups of physiological traits are the “units”, and that multiple groups may be very different in their details, yet differ little in their adaptive value. To put it simply, “there’s more than one way to skin a cat.” In such cases, heterozygotes (i.e., heterozygous for two groups of traits) may offer an advantage over either single group, as well as over any possible recombination of the unit characters. Lechowicz has been involved in some very interesting research along these lines. http://bulbnrose.x10.mx/Heredity/Lechowicz.html