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961.
962.
The compensatory response is a regulatory event influencing the redundancy of the ribosomal RNA cistrons (rDNAs) of Drosophila melanogaster. In this report we attempt to demonstrate that the compensatory event and the thymidine analogue bromodeoxyuridine (BrdU) specifically interact. We conclude that the drug inhibits the compensatory response of Drosophila melanogaster XO males and argue that the compensatory event is not the passive consequence of replicational dominance known to occur in Drosophila polytene tissues. 相似文献
963.
M. P. Koshy G. Namkoong J. H. Roberds 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1998,97(5-6):990-993
Either by selective breeding for population divergence or by using natural population differences, F2 and advanced generation hybrids can be developed with high variances. We relate the size of the genetic variance to the population
divergence based on a forward and backward mutation model at a locus with two alleles with additive gene action. The effects
of population size and initial gene frequency are also explored. Larger parental population sizes increase the F2 genetic variance if the initial probability distribution is uniform or U-shaped. However, population size has the opposite
effect if the initial distribution of gene frequencies is skewed such as it would be with newly arriving alleles. These alleles
contribute to the genetic variance sooner when the selection pressure is higher or when the effective population size is smaller.
Received: 5 April 1998 / Accepted: 22 April 1998 相似文献
964.
Suzanne Bourgeois 《Journal of cellular biochemistry》1980,13(3):401-410
The glucocorticoid-induced lysis of lymphoid cell lines offers a genetic approach to steroid hormone action because unresponsive variants can easily be selected as resistant to this lytic effect. The present state of analysis of lymphocytolysis in two murine cell lines, the S49 T-lymphoma and the W7 thymoma, is reviewed. All glucocorticoid-resistant variants isolated so far result from various defects in the glucocorticoid receptor. The absence of variants blocked at another step of the lytic mechanism is discussed. The observed hemizygosity of the glucocorticoid receptor locus in the S49 line and the instability of cell hybrids illustrate some of the potential problems encountered in somatic cell genetics. 相似文献
965.
Markus Risch und Lars Andersen 《Journal of Ornithology》1998,139(2):173-177
Zusammenfassung Die als Unterarten klassifizierten europäischen Formen der Aaskrähe, Rabenkrähe und Nebelkrähe, besiedeln verschiedene, aneinandergrenzende Verbreitungsgebiete und hybridisieren in der Kontaktzone. Die Nachkommen von Mischpaaren sind fruchtbar und können sowohl mit anderen Hybriden als auch mit Raben- und Nebelkrähen erfolgreich brüten. Trotzdem kommt es zu keiner völligen Vermischung der Formen und/oder Verlagerung der Verbreitungsgebiete. Vor diesem Hintergrund untersuchten wir die Partnerwahl von Aaskrähen in der Hybridisierungszone auf der nordfriesischen Insel Amrum und stellten fest, daß Partner gleichen Phänotyps häufiger miteinander verpaart waren, als stochastisch zu erwarten gewesen wäre. Unsere Daten bestätigen vergleichbare Studien aus Hybridisierungszonen in Italien und Sibirien. Wir schließen daraus, daß phänotypisch selektive Partnerwahl bei der Aaskrähe ein allgemeines Phänomen sein könnte und diskutieren, warum dieses Verhalten anfitness-relevante Parameter gekoppelt sein sollte. Um welche es sich dabei handeln könnte, wurde bisher nicht hinreichend untersucht und muß deshalb offen bleiben.
Non-random mating of Crows (Corvus corone) in a hybrid zone of Carrion Crow (C. c. corone) and Hooded Crow (C. c. cornix)
Summary Carrion Crow and Hooded Crow are regarded as subspecies of the Crow. They show frequent hybridisation along the adjacent borders of their distribution. Mixed pairs produce fertile offspring which are able to breed successfully with both hybrids and mates of either phenotype. However, hybridisation does not lead to phenotypic changes of Carrion and Hooded Crows in general nor in their distinct distribution. We studied the mating behaviour of Crows in the hybrid zone on the Island of Amrum (Schleswig-Holstein, Germany) and found evidence that Crows may prefer mates of the same phenotype. Our data confirm previous studies which reported assortative mating with respect to plumage coloration from hybrid zones in Italy and Siberia. We discuss why this behaviour should be related tofitness traits which in our opinion have not yet been studied adequately nor identified.相似文献
966.
967.
T E Broad D J Burkin L M Cambridge C Jones P E Lewis H G Morse D Geyer P D Pearce H A Ansari D W Maher 《Animal genetics》1995,26(2):85-90
Six loci, apoliproprotein B (including Ag(x) antigen), immunoglobulin kappa constant region (IGKC), luteinizing hormone/choriogonadotrophin receptor, avian myelocytomatosis viral related oncogene, neuroblastoma derived, ornithine decarboxylase, and proopiomelanocortin (adrenocorticotropin/beta-lipotropin) (POMC), were newly assigned to sheep chromosome 3p using a chromosomally characterized minipanel of sheep-hamster cell hybrids. Isotopic in situ hybridization of IGKC to sheep chromosome 3p22–p17 is reported, confirming the cell hybrid assignment. As these loci are all known to map to human chromosome 2p, this study demonstrates that this chromosomal segment is extensively conserved in sheep. Only POMC has been previously assigned to cattle chromosome 11, which is the equivalent of sheep chromosome 3p. Therefore, we predict that the other loci assigned in this study to sheep 3p are likely to be located on cattle 11. The provisional assignment of an additional locus, annexin-like to sheep chromosome 3p is also reported. 相似文献
968.
Luc De Meester 《Aquatic Ecology》1997,31(1):79-87
Zooplankton, Daphnia in particular, are increasingly used as model organisms to investigate general evolutionary biological questions. I here discuss some recent insights into the patterns and processes determining genetic diversity within and genetic differentiation among natural populations of cyclically parthenogenetic Daphnia. I focus on three aspects: (1) the interplay of phenotypic plasticity and genetic polymorphism in explaining variability in ecologically relevant traits, (2) the patterns of genetic variation revealed by neutral markers and ecologically relevant traits, and (3) the evolutionary ecological importance of hybridization events in Daphnia. The need for studies on the evolutionary ecology of sexual reproduction and dispersal via ephippial eggs in Daphnia is stressed. 相似文献
969.
A slot-blot method is described that provides rapid and reliable identification of somatic hybrids. Biotin-labelled probes
of defined length were prepared from genomic DNA, and calibrated in conjunction with target DNA to allow for differing amounts
of biotin incorporation and hybridisation efficiency. The presence of probe DNA was visualised by chemiluminescence detection.
Probes of 1 to 5 kbp in length gave optimal discrimination among target DNAs from different potato species. The advantages
of this method over existing ones are described. 相似文献
970.
Larval feeding was assayed in a generalist caterpillar (Heliothis virescens (F.)), a specialist caterpillar (Heliothis subflexa (Gn.)), their F1 hybrids and a backcross withH. s. to gain a preliminary understanding of the genetic basis of host use inH. v. Plants used in these experiments were tobacco (Nicotiana tabaccum), cotton (Gossypium hirsutum), soybean (Glycine max) (hosts ofH. v.) and ground cherry (Physalis pubescens) (host ofH.s.).
A feeding study ofH.v., H.s. and their reciprocal hybrids showed that, after the first eight days of feeding,H.v. had its highest survival and weight gain on soybean and had lowest survival and weight gain on its non-host,Physalis. H.s. had its highest survival and weight gain on its host plant,Physalis, and performed very poorly on the three non-host plants. The two F1 hybrids were SV0 (offspring ofH.s. female andH.v. male) and VS0 (offspring ofH.v. female andH.s. male). The hybrids did not differ from each other, indicating no sex linkage or maternal effects, except that VS0 had greater weight gain on tobacco than did SV0. The hybrids, unlike their parents, survived well on all four host plants and their weight gain was intermediate on all four
host plants.
In a separate experiment the VS0 hybrid was mated to the specialist to produce the VS1 backcross. In contrast to the F1, the backcross had significantly lower survival than the generalist on soybean, cotton, tobacco and weight gain was lower
on soybean, cotton and tobacco but higher onPhysalis. Survival and weight gain on cotton and tobacco were inherited as partially dominant traits; onPhysalis there was overdominance for survival and complete dominance for weight gain; on soybean both survival and weight gain were
additive. Survival on cotton,Physalis, soybean and tobacco and weight gain onPhysalis could not be completely explained by a model that included only dominance and additive effects. These traits may be influenced
by epistatic and/or environmental effects. 相似文献