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At least 199 records · Page 11Linked to original sources
PubMed2000

Effect of mating system, flushing procedure, progesterone dose and donor ewe age on the yield and quality of embryos within a MOET program in sheep.

Multiple ovulation and embryo transfer (MOET) has the potential to increase the rates of genetic improvement in sheep. However, better realization of this potential requires a higher yield of transferable embryos. Thus we investigated some factors that may contribute to high embryo yield and quality under field conditions, as part of an ongoing MOET program. Comparison of the effects of 2 breeding systems (natural service plus laparoscopic intrauterine AI vs natural service only) on embryo yield and quality indicated that while AI did not affect embryo recovery, it significantly (P < 0.05) improved fertilization rate and embryo quality, and increased (P < 0.05) embryo survival rate after transfer to recipients. Two flushing procedures (the original semi-laparoscopic and a modified version) were compared for effects on embryo recovery. The modifications made to the original collection method increased (P < 0.001) embryo recovery from 69.0 +/- 2.4 to 83.2 +/- 0.6%. The effects of the progestagen priming dosage during superovulatory treatment and ewe age on MOET outcome were also investigated. Donor ewes primed with 30-mg progestagen sponges came into estrus 1.9 h earlier (P < 0.05) than those primed with 45-mg sponges, but there was no difference in ovulation rate or embryo recovery, or in embryo survival after transfer between the 2 regimens. However, Chi-square analysis indicated a significant benefit in favor of the higher progesterone dose on both fertilization (P < 0.01) and embryo quality (P < 0.001). Age of donor ewe did not significantly affect the timing of estrus, fertilization rate or embryo survival after transfer. While adult ewes had higher (P < 0.05) ovulation rates and embryo yields, shearling ewes produced a much higher proportion of Grade 1 embryos (P < 0.05).

Aging↗
PubMed2004

Mating systems in the genus Xanthoria (lichen-forming ascomycetes).

Genetic variability among sterile cultured single ascospore isolates of Xanthoria parietina, X. calcicola, X. ectaneoides, X. capensis, X. polycarpa and X. resendei was investigated with RAPD-PCR. If available five out of eight ascospores per ascus were analysed. In some samples multispore and mycelial isolates from ascomata were included in the analysis. Ascospore germination rates and phenotypic features such as growth rate, pigmentation and secondary metabolites were uniform in X. parietina sporelings of the same ascus, but varied among the progeny of meiosis in all other species. Phenotypic features correlated with genetic variability. X. parietina revealed polymorphisms among specimens from different worldwide locations. In contrast nine out of ten sets of sibling spores were genetically uniform, with only 2% polymorphism in the remaining set, indicating that X. parietina might be homothallic. X. calcicola, X. ectaneoides, X. capensis, X. polycarpa and X. resendei revealed 9-66% polymorphic loci and therefore are considered heterothallic.

Ascomycota↗
PubMed1999

Cleistogamy in Scutellaria indica (Labiatae): effective mating system and population genetic structure.

Scutellaria indica is a perennial herb with both chasmogamous (CH) and cleistogamous (CL) flowers on the same plant in some populations, and only CL flowers in other populations. Actual seed production by CH and CL flowers was investigated in populations of S. indica. The average seed set of CL flowers was 19 times higher than CH flowers, indicating much greater fertilization success. The CL seeds were also significantly heavier than the CH seeds. However, the resource cost of producing a CH flower was much higher than that of producing a CL flower. The CH flower was approximately seven times larger, and its pollen/ovule ratio was approximately five times higher than flowers. The level and pattern of genetic diversity at both allozyme and random amplified polymorphic DNA (RAPD) levels were consistent with a predominantly selfing system in the species. The average amount of within-population genetic variation was extremely low (A = 1.025, P = 2.36%, HO = 0.001 and HE = 0.008 based on allozyme data, and P = 8.94% and HE = 0.03 based on RAPD data). At the species level, the estimates of total gene diversity (HT) were 0. 101 based on allozyme data and 0.139 based on RAPD data. A very high level of genetic differentiation occurred between populations (allozyme GST = 0.92 and RAPD GST = 0.81). Genetic drift coupled with predominant cleistogamous selfing apparently played the major role in determining the population genetic structure in S. indica. Although the features associated with CH and CL flower and seed production seem to be sufficient for the evolution of complete cleistogamy in S. indica, random fixation of alternative alleles for dimorphic or complete cleistogamy in small populations could maintain the multiple strategy of chasmogamous and cleistogamous reproduction in the species.

DNA Primers↗
PubMed2002

The influence of mating system, demography, parasites and colonization on the population structure of Biomphalaria pfeifferi in Madagascar.

Current evolutionary forces and historical processes interact to shape the distribution of neutral genetic variability within and among populations. Focusing on the genetics of recently introduced organisms offers a good opportunity to understand the relative importance of these factors. This study concerns variation at 8 polymorphic microsatellite loci in 30 populations of Biomphalaria pfeifferi. The sampling area spans most of the species' range in Madagascar where it was probably introduced recently. Extremely low variation was found within all populations studied, which may partly result from high selfing rates. However, this cannot account for the variance of variation across populations, which is better explained by habitat openness (that reflects environmental stochasticity), the prevalence of the parasitic trematode Schistosoma mansoni and historical demography (colonization and subsequent bottlenecks). Large global differentiation was also observed, suggesting that current gene flow among populations is limited to small distances, within watersheds and to few individuals. Our data set also allowed us to test several hypotheses regarding colonization, based on bottleneck and admixture tests. The observed pattern requires at least two independent introductions from slightly differentiated genetic sources in the western part of Madagascar. Another introduction, from a very different genetic origin, should also be postulated to explain the genetic composition of eastern populations. That this introduction occurred recently suggests that the colonization of Madagascar by B. pfeifferi is an ongoing process.

Animals↗
PubMed1991

Intraspecific variation in population gene diversity and effective population size correlates with the mating system in plants.

Published data on allele frequencies at isozyme loci in inbreeding and outbreeding plant species were analyzed to examine intraspecific variation in gene diversity and effective population size (Ne). Compared with outbreeders, inbreeding species showed markedly greater variation among populations in average values of Nei's gene diversity statistic. Effective population size was estimated by assuming that the variation observed at isozyme loci is selectively neutral. Inbreeding species showed greater levels of variation in Ne than did outbreeders, although the upper range of Ne was similar in the two classes of species. The results suggest that there may be considerable genetic variation and potential for evolutionary change in some but not all populations of inbreeders. Moreover, these findings are important with respect to the conservation of genetic resources. In particular, that the amount of intraspecific variation in population genetic diversity and Ne differs between inbreeding and outbreeding species should be taken into account in sampling efforts designed to optimize the diversity of germplasm collections.

Journal Article↗