Enfant à charge et parent isolé ou les difficultés de mise en oeuvre des critères de fait

1 vol. (237 p.) + Note de synthèse (18 p.)Le projet de recherche avait pour ambition d'apprécier le contentieux en matière de prestations familiales s'agissant de la mise en œuvre des dispositions de droit social qui font appel à un critère de fait plutôt que de se référer directement au statut civil. Ces critères de fait sont celui d'enfant à charge, et il concerne l'ensemble des prestations familiales, et celui de parent isolé s'agissant des prestations retenant cette qualification, soit l'allocation de parent isolé et l'allocation de soutien familial. Une première approche montrait que les caisses d'allocations familiales ont à l'évidence des difficultés pour mettre en œuvre les critères de fait propres au droit social qui veulent s'affranchir des catégories instituées du droit civil de la famille et une meilleure connaissance des pratiques instaurées à l'intérieur des Caisses semblait nécessaire d'une part afin de mieux connaître l'ampleur du contentieux soulevé par l'utilisation du critère d'enfant à charge ou par l'utilisation du critère d'isolement, d'autre part afin de mieux appréhender l'autonomie des caisses dans la mise en œuvre de la règle de droit. Il s'agissait donc de préciser les modalités d'application de ces critères de fait et de rechercher les modes d'élaboration des pratiques instituées à l'intérieur des caisses d'allocations familiales

Population structure and genetic diversity in a commercial maize breeding program assessed with SSR and SNP markers

Information about the genetic diversity and population structure in elite breeding material is of fundamental importance for the improvement of crops. The objectives of our study were to (a) examine the population structure and the genetic diversity in elite maize germplasm based on simple sequence repeat (SSR) markers, (b) compare these results with those obtained from single nucleotide polymorphism (SNP) markers, and (c) compare the coancestry coefficient calculated from pedigree records with genetic distance estimates calculated from SSR and SNP markers. Our study was based on 1,537 elite maize inbred lines genotyped with 359 SSR and 8,244 SNP markers. The average number of alleles per locus, of group specific alleles, and the gene diversity (D) were higher for SSRs than for SNPs. Modified Roger’s distance (MRD) estimates and membership probabilities of the STRUCTURE matrices were higher for SSR than for SNP markers but the germplasm organization in four heterotic pools was consistent with STRUCTURE results based on SSRs and SNPs. MRD estimates calculated for the two marker systems were highly correlated (0.87). Our results suggested that the same conclusions regarding the structure and the diversity of heterotic pools could be drawn from both markers types. Furthermore, although our results suggested that the ratio of the number of SSRs and SNPs required to obtain MRD or D estimates with similar precision is not constant across the various precision levels, we propose that between 7 and 11 times more SNPs than SSRs should be used for analyzing population structure and genetic diversity

Molecular and Historical Aspects of Corn Belt Dent Diversity

Tens-of-thousands of open-pollinated cultivars of corn (Zea mays L.) are being maintained in germplasm banks. Knowledge of the amount and distribution of genetic variation within and among accessions can aid end users in choosing among them. We estimated molecular genetic variation and looked for influences of pedigree, adaptation, and migration in the genetic makeup of conserved Corn-Belt Dent-related germplasm. Plants sampled from 57 accessions representing Corn-Belt Dents, Northern Flints, Southern Dents, plus 12 public inbreds, were genotyped at 20 simple sequence repeat (SSR) loci. For 47 of the accessions, between 5 and 23 plants per accession were genotyped (mean = 9.3). Mean number of alleles per locus was 6.5 overall, 3.17 within accessions, and 3.20 within pooled inbreds. Mean gene diversity was 0.53 within accessions and 0.61 within pooled inbreds. Open-pollinated accessions showed a tendency toward inbreeding (FIS = 0.09), and 85% of genetic variation was shared among them. A Fitch-Margoliash tree strongly supported the distinctiveness of flint from dent germplasm but did not otherwise reveal evidence of genetic structure. Mantel tests revealed significant correlations between genetic distance and geographical (r = 0.54, P= 0.04) or maturity zone (r = 0.33, P = 0.03) distance only if flint germplasm was included in the analyses. A significant correlation (r = 0.76, P \u3c 0.01) was found between days to pollen shed and maturity zone of accession origin. Pedigree, rather than migration or selection, has most influenced the genetic structure of the extant representatives of the open-pollinated cultivars at these SSR loci

Participation au 2ème séminaire de recherche du projet ANR Profam

National audienc

Evaluation de la contribution à l’entretien de l’enfant et table de référence

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