Fine-mapping of a region of variation in recombination rate on BTA23 to the D23S22-D23S23 interval using sperm typing and meiotic breakpoint analysis

Meiotic recombination rate (θ) within chromosome segments of similar physical size is known to vary widely throughout the genome. This variation has a genetic component, occurring between the sexes and among individuals of the same sex. We reported previously the existence of variation in θ between males in the DYA-PRL interval on bovine chromosome 23 (BTA23). This region contains the bovine major histocompatibility complex and has been shown to contain recombination hotspots in humans and mice. The aim of this study was to map more finely the interval(s) on BTA23 where variation in θ occurs using sperm typing and meiotic breakpoint analysis. By adding a marker (DRB3) between DYA and PRL, the DYA-PRL interval was subdivided into two adjacent intervals, thus permitting evaluation and comparison of θ among five bulls. Significant variation in θ was found for both intervals; θ(DYA-DRB3) ranged from 13.2 to 28.1%, and θ(DRBS-PRL) ranged from 2.4 to 13.0%. The variation in θ was individual- and region-specific. A meiotic breakpoint strategy employing PCR amplification products from recombinant sperm was then used to refine the chromosomal location associated with variation in θ within the DYA-DRB3 interval. The subinterval D23S22-D23S23 exhibited the greatest degree of variation among bulls having high and low θ within the DYA-DRB3 interval. To confirm this result, θ(D23S22-D23S23) was directly evaluated in three additional randomly chosen bulls using sperm typing. The region showing variation in θ was narrowed to the D23S22-D23S23 subinterval, ranging from 4.6 to 9.2%. Identification of the molecular basis for variation in θ may be useful for map-dependent applications, such as marker-assisted selection and positional cloning of genes affecting physiologically important traits.