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71.
Most of the genetic divergence that currently separates populations of Homo sapiens must have arisen during that long period when the local village (or band) was the basic unit of biological evolution. Studies of tribally intact Amerindian groups exhibiting such small-group organization have demonstrated marked genetic divergence between nearby villages. Some of this genetic radiation can be attributed to the effects of random genetic drift over time within these small demes. Some of it, however, might be better ascribed to the consequences of nonrandom genetic assortment at the time of village fission, a recurring event for such groups. Even random genetic assortment at the time of fission would lead to some genetic divergence, due to the finite size of the parent gene pool. We term the genetic consequences of random assortment the random fission effect. Routinely, village fission occurs along family lines, leading to even greater genetic divergence between the daughter villages. We use the term lineal fission effect to describe the genetic consequences of nonrandom assortment and contrast these results with those derived from random assortment.——A formal treatment of random and lineal fission effects is developed, first for the single-locus case, then for the multiple-locus extension. Using this formulation, three Yanomama fission events were examined. Fission in the Yanomama often involves a great deal of mutual hostility between the two factions, so that subsequent gene flow between the two daughter villages is minimal. The first two examples are typical of the Yanomama behavior norm, and are accompanied by a minimum of subsequent gene flow between the daughter villages. In these two cases, the observed divergence values are very large and are also very unlikely under random fission. The lineal fission effect is pronounced. The net impact of lineal fission is to reduce the effective size of the village at the time of fission by a factor of four, relative to expectation from random fission. The third example, however, involved an unusually amicable split of a village, followed by free genetic exchange between the fission products. This "friendly fission" yields an observed divergence value not much in excess of the expectation from random fission.—The long-term consequences of such fission bottlenecks in effective population size are discussed for both intra- and inter-tribal genetic diversity. It appears that the rate of genetic divergence for tribal and subtribal groups may have been somewhat greater than would be expected from classical drift arguments. 相似文献
72.
Virginia Brothers Barbara ONeill Rowley Theo Gerritsen 《Archives of biochemistry and biophysics》1975,166(2):475-482
The effects of vitamin B12 deficiency in rats and dietary supplementation with vitamin B12 and/or l-methionine plus folate on the oxidation of compounds metabolized through folate coenzyme pathways were investigated. Rats fed a vitamin B12-deficient diet oxidized significantly lower amounts in 60 min of l-histidine, glycine, sarcosine, formate, and l-serine to CO2 than vitamin B12-supplemented controls. Supplementation of the deficient diet with l-methionine plus folate restored the ability to oxidize the ring-2-carbon of l-histidine, the methyl group of sarcosine, and formate to the same level as that observed in animals receiving vitamin B12. In contrast, oxidation of the 1-carbon of glycine and the 3-carbon of l-serine was not restored to control levels by addition of methionine plus folate to the vitamin B12-deficient diet. Inhibition of the metabolism of the 2-carbon of glycine to CO2 was partially overcome by additional dietary methionine and folate. Glycine synthase activity in homogenates paralleled the in vivo pattern of oxidation of the 1-carbon of glycine to CO2, whereas sarcosine dehydrogenase activity appeared to increase 2-fold in vitamin B12 deficiency. 相似文献
73.
Using sensitive radio-enzymatic assays, levels of plasma total catecholamines and norepinephrine in rats change dramatically with changes in body temperature. The decrease in plasma catecholamines induced by warming the animal is reflected in an apparent arterio-venous difference when arterial blood is obtained at room temperature and tail sampling is aided by heat induced vasodilation. Combined blockade of extraneuronal and neuronal uptake reduces this arterio-venous difference. Blood samples obtained from the decapitated trunk of the rat contain similar levels of plasma catecholamines as those obtained from indwelling carotid catheters. Blood levels of dopamine-betahydroxylase were similar whether obtained by venous sampling during heat-induced vasodilation, decapitation or indwelling arterial cannula. 相似文献
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75.
A genetic analysis of an array of mitomycin-induced rearrangements in immature Drosophila oocytes is reported. Induced aberrations were recovered representing detachments of the compound-X chromosome, Y chromosome fragments, X chromosome loss and mosaicism. The spectrum of rearrangements induced by mitomycin C was very similar to that induced by X-ray treatment of immature oocytes. This work suggests that mitomycin C has two modes of action. The drug is radiomimetic for it induces the types of aberrations recovered after X-irradiation. Mitomycin C also seems to have a delayed effect which is reflected in the relatively high recovery of mosaics. 相似文献
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77.
Suzanne M. Marselis Katharine Abernethy Alfonso Alonso John Armston Timothy R. Baker Jean‐Francois Bastin Jan Bogaert Doreen S. Boyd Pascal Boeckx David F. R. P. Burslem Robin Chazdon David B. Clark David Coomes Laura Duncanson Steven Hancock Ross Hill Chris Hopkinson Elizabeth Kearsley James R. Kellner David Kenfack Nicolas Labrire Simon L. Lewis David Minor Herv Memiaghe Abel Monteagudo Reuben Nilus Michael O'Brien Oliver L. Phillips John Poulsen Hao Tang Hans Verbeeck Ralph Dubayah 《Global Ecology and Biogeography》2020,29(10):1799-1816
78.
Donato Santovito Virginia Egea Kiril Bidzhekov Lucia Natarelli Andr Mouro Xavier Blanchet Kanin Wichapong Maria Aslani Coy Brunßen Michael Horckmans Michael Hristov Arie Geerlof Esther Lutgens Mat J. A. P. Daemen Tilman Hackeng Christian Ries Triantafyllos Chavakis Henning Morawietz Ronald Naumann Philipp Von Hundelshausen Sabine Steffens Johan Duchêne Remco T. A. Megens Michael Sattler Christian Weber 《Autophagy》2020,16(12):2294
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80.
Integrated requirement of non‐specific and sequence‐specific DNA binding in Myc‐driven transcription