A Developmental Study of Maize with Particular Reference to Hybrid Vigor

Weaver, Harry Lloyd

doi:10.2307/2437404

Cited by 2 publications

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“…Structural diflferences between inbreds and heterotic hybrids shown by the studies of Burkholder and McVeigh (1940), Weaver (1946), and the members of our laboratory (Whaley et al, 1950;Heimsch et al, 1950;Rabideau ef al., 1950) are apparently to be regarded as results of heterosis rather than as causal factors. The evidence suggests that heterosis is concerned primarily with growth processes and that differentiation activities are most likely involved secondarily rather than primarily.…”

Section: The Physiological Basis Of Heterosismentioning

confidence: 77%

Heterosis : a record of researches directed toward explaining and utilizing the vigor of hybrids

Gowen¹

1952

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CONWAY ZIRKLEexception. Practically all of its factual background was reported before Mendel's great contribution was discovered. Even workable methods for utilizing hybrid vigor in crop production were known, but it was not until the classic post-Mendelian investigations of Shull, East, and Jones were completed, that heterosis took its proper place in genetics. The following discussion of the importance of heterosis will be confined to its pre-Mendelian background.Heterosis can be described as a special instance of the general principles involved in inbreeding and outbreeding. To fit it into its proper niche, we will trace first the evolution of our ideas on the effects of these two contrasting types of mating. Since our earliest breeding records seem limited to those of human beings and primitive deities, we will start with the breeding records of these two forms.Hybrid vigor has been recognized in a great many plants during the last two hundred years. We will therefore describe briefly what was known of its influence on these plants. Because heterosis has reached its greatest development in Zea mays, we will trace briefly the pre-Mendelian genetics of this plant, and show how the facts were discovered which have been of such great scientific and economic importance.The ill effects of too-close inbreeding have been known for a long time.Indeed, Charles Darwin (1868) believed that natural selection had produced in us an instinct against incest, and was effective in developing this instinct because of the greater survival value of the more vigorous offspring of exogamous matings. One of his contemporaries, Tylor (1865), noted that many savage tribes had tabooed the marriage of near relatives, and he assumed that they had done so because they had noticed the ill effects of inbreeding. The Greeks looked upon certain marriages between near relatives as crimes. This has been known almost universally ever since Freud popularized the tragedy of King Oedipus. At present, we outlaw close inbreeding in man, and our custom is scientifically sound.We are apt to be mistaken, however, if we read into the standards of our distant preceptors the factual knowledge which we have today. The intellectual ancestors of European civilization approved of inbreeding and actually practiced it on supposedly eugenic grounds. The fact that their genetics was unsound and their eugenic notions impractical is irrelevant.They had their ideals, they were conscientious and they did their duties. The Pharaohs married their own sisters when possible so that their godlike blood would not be diluted. Marriage between half brother and sister was common in other royal families of the period. Actually, as we shall see, the two great pillars of European thought, Hebrew morality and Greek philosophy, endorsed inbreeding as a matter-of-course.The Hebrews, who derived mankind from a single pair, were compelled to assume that the first men born had to marry their sisters-as there were EARLY IDEAS ON INBREEDING AND CROSSBREEDING 3 then no other women on the e...

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Section: The Physiological Basis Of Heterosismentioning

confidence: 77%