Augmentation of the antibody response by hapten help: I. Dominant genetic control

The objective of the present work was to characterize those genetic factors that determine susceptibility to “hapten help,” i.e., the augmentation of B-cell responses by hapten-reactive T cells. After mice had been sensitized to the hapten azobenzenearsonate (ABA), one of two approaches was used to assay hapten help. In the first, circumvention of tolerance to low doses of bovine γ-globulin (BGG) was augmented in CBA but not in C57BL/6 mice, as measured by serum anti-BGG antibody after challenge with ABA-BGG. Second, similar strain differences but on a larger scale were demonstrated in the anti-BGG plaque-forming cell (PFC) response of spleen cells from hapten-primed nontolerized mice after challenge with ABA-BGG. Results with the F1-hybrid of a cross between a high responder and a low responder for hapten help demonstrated that high responsiveness is dominant. Experiments with recombinant inbred mice from high- and low-responder progenitor strains suggested that hapten help is associated not with the major histocompatibility complex (H-2) so much as with minor histocompatibility antigens such as H-22 and/or H-24, both of which are on chromosome 7.     

A unified model for complex segregation analysis.

Various methods have been proposed for statistical inference of major genes by segregation analysis of human familial data. An attempt is made to resolve some divergences that have occurred in this context by the consideration of a unified model, with some practical applications.     

Genetic diversity and selection signatures in maize landraces compared across 50 years of in situ and ex situ conservation

Genomics-based, longitudinal comparisons between ex situ and in situ agrobiodiversity conservation strategies can contribute to a better understanding of their underlying effects. However, landrace designations, ambiguous common names, and gaps in sampling information complicate the identification of matching ex situ and in situ seed lots. Here we report a 50-year longitudinal comparison of the genetic diversity of a set of 13 accessions from the state of Morelos, Mexico, conserved ex situ since 1967 and retrieved in situ from the same donor families in 2017. We interviewed farmer families who donated in situ landraces to understand their germplasm selection criteria. Samples were genotyped by sequencing, producing 74,739 SNPs. Comparing the two sample groups, we show that ex situ and in situ genome-wide diversity was similar. In situ samples had 3.1% fewer SNPs and lower pairwise genetic distances (F_st 0.008–0.113) than ex situ samples (F_st 0.031–0.128), but displayed the same heterozygosity. Despite genome-wide similarities across samples, we could identify several loci under selection when comparing in situ and ex situ seed lots, suggesting ongoing evolution in farmer fields. Eight loci in chromosomes 3, 5, 6, and 10 showed evidence of selection in situ that could be related with farmers’ selection criteria surveyed with focus groups and interviews at the sampling site in 2017, including wider kernels and larger ear size. Our results have implications for ex situ collection resampling strategies and the in situ conservation of threatened landraces.Subject terms: Agricultural genetics, Population genetics