2 results
Genome-wide analysis in endangered populations: a case study in Barbaresca sheep
- S. Mastrangelo, B. Portolano, R. Di Gerlando, R. Ciampolini, M. Tolone, M. T. Sardina, The International Sheep Genomics Consortium
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Analysis of genomic data is becoming increasingly common in the livestock industry and the findings have been an invaluable resource for effective management of breeding programs in small and endangered populations. In this paper, with the goal of highlighting the potential of genomic analysis for small and endangered populations, genome-wide levels of linkage disequilibrium, measured as the squared correlation coefficient of allele frequencies at a pair of loci, effective population size, runs of homozygosity (ROH) and genetic diversity parameters, were estimated in Barbaresca sheep using Illumina OvineSNP50K array data. Moreover, the breed’s genetic structure and its relationship with other breeds were investigated. Levels of pairwise linkage disequilibrium decreased with increasing distance between single nucleotide polymorphisms. An average correlation coefficient <0.25 was found for markers located up to 50 kb apart. Therefore, these results support the need to use denser single nucleotide polymorphism panels for high power association mapping and genomic selection efficiency in future breeding programs. The estimate of past effective population size ranged from 747 animals 250 generations ago to 28 animals five generations ago, whereas the contemporary effective population size was 25 animals. A total of 637 ROH were identified, most of which were short (67%) and ranged from 1 to 10 Mb. The genetic analyses revealed that the Barbaresca breed tended to display lower variability than other Sicilian breeds. Recent inbreeding was evident, according to the ROH analysis. All the investigated parameters showed a comparatively narrow genetic base and indicated an endangered status for Barbaresca. Multidimensional scaling, model-based clustering, measurement of population differentiation, neighbor networks and haplotype sharing distinguished Barbaresca from other breeds, showed a low level of admixture with the other breeds considered in this study, and indicated clear genetic differences compared with other breeds. Attention should be given to the conservation of Barbaresca due to its critical conservation status. In this context, genomic information may have a crucial role in management of small and endangered populations.
2 - Pollen development and pollen–pistil interaction
- Edited by K. R. Shivanna, University of Delhi, V. K. Sawhney, University of Saskatchewan, Canada
- Foreword by R. Bruce Knox
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- Book:
- Pollen Biotechnology for Crop Production and Improvement
- Published online:
- 11 September 2009
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- 13 April 1997, pp 15-39
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Summary
Summary
Structural details of pollen development are quite uniform in most of the species studied. The main structural events associated with pollen development are (i) the formation of a syncytium of microspore mother cells (MMCs), also referred to as pollen mother cells (PMCs) or meiocytes, in each anther locule, followed by the isolation of each MMC and the resulting microspores encased in a callose wall; (ii) cytoplasmic reorganization resulting in the breakdown of most of the RNA and ribosomes of MMCs, and de-differentiation of plastids and mitochondria; (iii) release of microspores by the activation of callase; (iv) development of microspores accompanied by the synthesis and buildup of RNA, ribosomes, and proteins, and redifferentiation of plastids and mitochondria; (v) asymmetric division of the microspore; and (vi) desiccation and dispersal of pollen grains. The tapetum undergoes several changes and plays a crucial role in pollen development. Although the pistil shows tremendous morphological diversity, the surface of the stigma and the path of pollen tube growth in the pistil invariably contain extracellular components that come into contact with the pollen grain and the pollen tube. Pollination initiates a series of events leading to the discharge of sperm cells in the embryo sac and double fertilization. There is a close interaction between pollen and pistil throughout the postpollination period, and so far only a beginning has been made in understanding the details of these interactions.
Introduction
The development of normal, viable pollen grains, their transfer to the stigma, and pollen germination and successful completion of pollen–pistil interaction are prerequisites for fruit and seed development. Since the beginning of this century, extensive studies have been carried out on various aspects of pollen biology.