D. L. Nash

Relative roles of mutation and recombination in generating allelic polymorphism at an MHC class II locus in Peromyscus maniculatus

The MHC class II loci encoding cell surface antigens exhibit extremely high allelic polymorphism. There is considerable uncertainty in the literature over the relative roles of recombination and de novo mutation in generating this diversity. We studied class II sequence diversity and allelic polymorphism in two populations of Peromyscus maniculatus, which are among the most widespread and abundant mammals of North America. We find that intragenic recombination (or gene conversion) has been the predominant mode for the generation of allelic polymorphism in this species, with the amount of population recombination per base pair exceeding mutation by at least an order of magnitude during the history of the sample. Despite this, patchwork motifs of sites with high linkage disequilibrium are observed. This does not appear to be consistent with the much larger amount of recombination versus mutation in the history of the sample, unless the recombination rate is highly non-uniform over the sequence or selection maintains certain sites in linkage disequilibrium. We conclude that selection is most likely to be responsible for preserving sequence motifs in the presence of abundant recombination.

Relationship of Dough Extensibility to Dough Strength in a Spring Wheat Cross

ABSTRACT A negative relationship between dough strength and dough extensibility would pose a problem for breeding hard wheats, as both dough strength and dough extensibility are desirable. We derived 77 recombinant inbred lines (RIL) from a cross between hard red spring wheat cultivars McNeal and Thatcher. McNeal produces flour with stronger dough and lower extensibility than does Thatcher. RIL were evaluated for strength-related properties using mixograph analysis and extensibility parameters using the Kieffer attachment to the TA.XT2 texture analyzer. Additionally, the RIL were test baked. Measurements using the mixograph and the Kieffer attachment were highly heritable. Maximum dough extensibility (Extmax) was negatively correlated with resistance to extension (Rmax) (r = -0.74) and with mixograph tolerance (r = -0.45). Loaf volume was correlated with both Rmax (r = 0.42) and area under the extensigraph curve (r = 0.44) based on partial correlation analysis adjusted for protein differences. Extmax was ...

Hard White Versus Hard Red Wheats: Taste Tests and Milling and Baking Properties

ABSTRACT Molecular markers for the red grain color (R) loci controlling seed color and the polyphenol oxidase (Ppo-A1) locus controlling polyphenol oxidase (PPO) activity in seed have recently been developed. These markers provided the opportunity to convert the hard red spring wheat cultivars Choteau and Hank to white-seeded versions with high and low PPO levels, respectively. These sets of near-isogenic lines provided material to test the effects of seed color and PPO activity on a range of end-use quality traits. We tested recurrent parents Choteau and Hank, along with near-isogenic derivatives with white seed, in two replicated trials in Bozeman, Montana, for end-use quality parameters. The white-seeded lines consisted of both high- and low-PPO near-isogenic lines. The primary impact of white seed was the production of whole wheat bread with a perceived sweeter taste relative to the red-seeded lines. Noodle color was not consistently impacted by the level of PPO variation despite relatively large redu...