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S ummary : Growth in soils of Mycobacterium paraffinicum with 0, 5, 15, 45 and 270 p/m of ethane was assayed by adding ethane-1,2-14 C and measuring the 14 CO2 produced. With < 45 p/m of ethane the lag period lasted several months. Differences in growth associated with different soils suggest that the microbial method of oil prospecting is unlikely to be commercially successful. 相似文献
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Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews
(genus Sorex) for the region between the tRNA(Pro) and the conserved
sequence block-F revealed variable numbers of 79-bp tandem repeats. These
repeats were found in all 19 individuals sequenced, representing three
subspecies and one closely related species of the masked shrew group (Sorex
cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an
outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an
adjacent 76-bp imperfect copy of the tandem repeats. One individual was
heteroplasmic for length variants consisting of five and seven copies of
the 79-bp tandem repeat. The sequence of the repeats is conducive to the
formation of secondary structure. A termination-associated sequence is
present in each of the repeats and in a unique sequence region 5' to the
tandem array as well. Mean genetic distance between the masked shrew taxa
and the pygmy shrew was calculated separately for the unique sequence
region, one of the tandem repeats, the imperfect repeat, and these three
regions combined. The unique sequence region evolved more rapidly than the
tandem repeats or the imperfect repeat. The small genetic distance between
pairs of tandem repeats within an individual is consistent with a model of
concerted evolution. Repeats are apparently duplicated and lost at a high
rate, which tends to homogenize the tandem array. The rate of D- loop
sequence divergence between the masked and pygmy shrews is estimated to be
15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid
sequence evolution in shrews may be due either to their high metabolic rate
and short generation time or to the presence of variable numbers of tandem
repeats.
相似文献
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大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育 总被引:1,自引:0,他引:1
本实验用免疫组织化学ABC法研究了大鼠胼胝体内神经肽Y免疫反应阳性(NPY-IR)纤维的生后发育。结果发现,许多NPY-IR纤维在大鼠出生时便存在于胼胝体内。NPY-IR胼胝体纤维的密度在生后1周内继续逐渐增高,在第2周内达到最高峰。之后,NPY-IR胼胝体纤维的密度逐渐下降,至第3周末时接近成年时的水平,即仅有少量NPY-IR纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多NPY-IR胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。 相似文献
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Ladd E. Johnson 《Hydrobiologia》1995,312(2):139-146
Zooplankton with calcareous skeletons are birefringent under cross-polarized light, and thus this technique can be quite useful, indeed sometimes almost essential, for the detection and enumemeration of these types of organisms in plankton samples. A simple and inexpensive application of this technique is described and illustrated with quantitative examples from research on the veligers of the zebra mussel Dreissena polymorpha (Pallas). The time required to detect veligers in plankton samples was decreased by an order of magnitude; the accuracy of counts was substantially improved (15% more than controls), and the time required for counts was greatly reduced (41% of control times). This technique is especially useful in situations in which veligers are difficult to find or see (e.g., at low densities, in samples cluttered with extraneous organisms or material) or when the investigator is inexperienced with plankton sampling and planktonic organisms. The major limitations are its inability to discriminate among various bivalve species that have planktonic larvae and the similar appearance of ostracods which also have calcareous shells. Expanded use of this technique should (1) increase our ability to use plankton sampling for the early detection of veligers during range expansion and reproductive cycles and (2) permit more accurate estimates of veliger abundance. 相似文献
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K. K. Wu D. J. Heinz H. K. Meyer S. L. Ladd 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1980,56(6):241-244
Summary Five Hawaiian commercial sugarcane (Saccharum sp. hybrids) clones were crossed in a full diallel. Four morphological characters were studied in the progeny: number of millable stalks per plant, stalk diameter, stalk length, and sucrose content. A fifth character, plant volume, was calculated from stalk number, stalk diameter and stalk length. The five selected parental clones were treated as fixed variables in the analysis. General combining ability (gca) was significant for all five characters; specific combining ability (sca) was significant for stalk diameter, stalk length, and plant volume. The variance for gca was large in all progeny populations. However, the variance for sca was large in the progeny of only some clones and/or for some individual characters. Parents were evaluated on the basis of their general combining ability: clone H49-3533 had high gca for sucrose content, while clone H53-5356 had high gca for plant vigor.Published with the approval of the Director as Journal Series Paper No. 455, Experiment Station, Hawaiian Sugar Planters' Association. 相似文献
9.
K. K. Wu D. J. Heinz H. K. Meyer S. L. Ladd 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1977,51(1):29-33
Summary An approximate method to determine sample size for the estimation of population variance, 2, is given. The estimate of 2 is denoted as s2 . Based on the assumption of a normal distribution for (s2/2–1), the sample size is approximately equal to 20,000 z2
p,/k2; where z is a standard normal deviate, p is the probability that s2 ( 100¦s2 – 2¦/2) is less than, or equal to, a critical value k, and k (measured as gDs2) is the desired precision of s2 .The expected value of s2, with respect to sample size, and the expected cumulative frequencies of s2 over sample size for various k values are given. Their goodness of fit to the observed results was satisfactory except for populations that were different from normal. The observed values were taken from a study on four yield components in five sugarcane polycross progenies, grown in two contrasting environments over 2 years in three selection stages.The expected s2 was found to be independent of the population coefficient of variance.Research suppoted in part by USDA, ARS, grant #12-14-5001-34. Published with the approval of the Director as Paper No. 412 in the Journal Series of the Experiment Station, Hawaiian Sugar Planters' Association. 相似文献
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