Assessment of mating management effect on genealogical parameters highlighting the genetic variability in a not closed fat-tailed Barbarine sheep pedigree

The Barbarine sheep is generally managed within small interconnected herds. The goal of the present work is to investigate the effect of the mating management on genetic variability in a registered flock which starts showing a productivity falling, especially in lamb’s survival and this despite a practice of outbreeding. Pedigree data of 11136 animals born between 1977 and 2007 were used to compute genealogical parameters. A first investigation of the lambs-parents relationships highlighted two periods that we denoted: P1 and P2. During P1, the mating strategy had been progressively based on animals born within the flock, whereas during P2, ewes and rams coming from outside the herd were gradually introduced as parents with unknown genealogy. This change in matings policy has been emphasised by plotting equivalent complete generations averaged whether by year of birth or maximum number of traced generations. All the computed genealogical parameters have been affected by the matings policy change and especially the individual average relatedness and realised effective size, which seem to be powerful tools to monitor the genetic variability within a population that is not closed to exchanges. An important effect of pedigree depth has been detected; this would require special attention to the matings of individuals with deepest genealogy. In spite of this effect, the heterozygote deficiency within the herd confirmed that the genetic variability has not been much affected along the flock life, which confirms that the decline in productivity should not be allotted to matings’ policy, but probably to other management factors.

Microsatellite variability and heterozygote deficiency in the arctic–alpine Alaskan wheatgrass (Elymus alaskanus) complex

Genetic variation in the allotetraploid grass Elymus alaskanus complex was assessed using microsatellites in seven populations from Canada, Greenland, and the U.S.A. Microsatellite variation was compared with allozyme and RAPD variation. Our results indicated that E. alaskanus was highly homozygous but also highly variable. The polymorphic loci ranged from 50 to 100% with a mean of 78.6%, and the mean number of allele per locus was 3.14. Average expected heterozygosity value (HE, gene diversity) varied across populations and ranged from 0.244 to 0.651 with mean of 0.414. The mean value of HE across Canadian populations (0.517) was significantly higher than that across populations in Greenland (0.367). The correlation between allozyme and microsatellite gene diversity value (HE) showed a high positive correlation (r = 0.68), but between RAPD and microsatellite showed a low positive correlation (r = 0.08). Populations were highly differentiated, with 38% of variation among populations. Interpopulation genetic distance showed no association with geographic distance between the population sites of origin. A Hardy-Weinberg exact test for all loci and all populations reveals a significant heterozygote deficiency. Possible explanations for heterozygote deficiency are discussed.Key words: Elymus alaskanus, microsatellites, heterozygote deficiency, genetic differentiation, variability.