Impact of candidate sire number and sire relatedness on DNA polymorphism-based measures of exclusion probability and probability of unambiguous parentage.

Genetic paternity testing can provide sire identity data for offspring when females have been exposed to multiple males. However, correct paternity assignment can be influenced by factors determined in the laboratory and by size and genetic composition of breeding groups. In the present study, DNA samples from 26 commingled beef bulls and their calves from the Nebraska Reference Herd-1 (NRH1), along with previously reported Illinois Reference/Resource Families data, were used to estimate the impact of sire number and sire relatedness on microsatellite-based paternity testing. Assay performance was measured by exclusion probabilities and probabilities of unambiguous parentage (PUP) were derived. Proportion of calves with unambiguous parentage (PCUP) was also calculated to provide a readily understandable whole-herd measure of unambiguous paternity assignment. For NRH1, theoretical and observed PCUP values were in close agreement (85.3 and 85.8%, respectively) indicating good predictive value. While the qualitative effects on PUP values of altering sire number and sire relatedness were generally predictable, we demonstrate that the impacts of these variables, and their interaction effects, can be large, are non-linear, and are quantitatively distinct for different combinations of sire number and degree of sire relatedness. In view of the potentially complex dynamics and practical consequences of these relationships in both research and animal production settings, we suggest that a priori estimation of the quantitative impact of a given set of interacting breeding group-specific and assay-specific parameters on PUP may be indicated, particularly when candidate sire pools are large, sire relatedness may be high, and/or loci numbers or heterozygosity values may be limiting.

Fine structure DNA mapping studies of the chromosomal region harboring the genetic defect in neurofibromatosis type I.

To better map the location of the von Recklinghausen neurofibromatosis (NF1) gene, we have characterized a somatic cell hybrid designated 7AE-11. This microcell-mediated, chromosome-transfer construct harbors a centromeric segment and a neo-marked segment from the distal long arm of human chromosome 17. We have identified 269 cosmid clones with human sequences from a 7AE-11 library and, using a panel of somatic cell hybrids with a total of six chromosome 17q breakpoints, have mapped 240 of these clones on chromosome 17q. The panel included a hybrid (NF13) carrying a der(22) chromosome that was isolated from an NF1 patient with a balanced translocation, t(17;22) (q11.2;q11.2). Fifty-three of the cosmids map into a region spanning the NF13 breakpoint, as defined by the two closest flanking breakpoints (17q11.2 and 17q11.2-q12). RFLP clones from a subset of these cosmids have been mapped by linkage analysis in normal reference families, to localize the NF1 gene more precisely and to enhance the potential for genetic diagnosis of this disorder. The cosmids in the NF1 region will be an important resource for testing DNA blots of large-fragment restriction-enzyme digests from NF1 patient cell lines, to detect rearrangements in patients' DNA and to identify the 17;22 NF1 translocation breakpoint.

Accessible intrachain disulfide bonds in hybrids of light chains.

The three-dimensional structure of the Mcg lambda-type Bence-Jones dimer crystallized in ammonium sulfate is known at 2.3-A resolution. A series of nine other human lambda-chains and two kappa-chains did not crystallize under the same conditions. After these proteins were hybridized with the Mcg light chain by the method of Peabody et al. [Biochemistry, 19, 2827 (1980)], however, crystals of six heterodimers were produced. Two of these (Mcg X Weir and Mcg X Hud) were suitable for X-ray analysis. The non-Mcg parental molecules in four of the crystallizable hybrids showed aberrant electrophoretic behavior after treatment with mild reducing agents. The results suggest that the intrachain disulfide bond in at least one domain (probably the variable domain) was susceptible to mild reductive cleavage in a significant proportion of light chains. Moreover, the loosening of the domain structure resulting from such disulfide cleavage in one parent appeared to promote the tendency of a hybrid molecule to crystallize.