Whole-genome regression methods have recently been extended to joint analysis of multiple traits, for investigation of mechanismssuch as pleiotropy-that cause trait associations. Gianola et al. show that a genomic correlation derived from molecular markers cannot always be interpreted as a genetic correlation. Without knowledge of linkage disequilibrium relationships between trait loci, and between trait loci and markers, speculating about genetic correlation and pleiotropy using genomic data
... sing genomic data is conjectural. Organisms on islands often evolve unusual body sizes. Little is known about the genetic basis of this intriguing pattern. Gray et al. demonstrate that Gough Island house mice-which are among the largest wild house mice in the world-rapidly evolved their exceptional size through a large number of genetic changes with individually modest effects. These results reveal that size evolution in nature is genetically complex, even when extreme changes happen on a short time scale. Transgenerational effects of early life starvation on growth, reproduction, and stress resistance in Caenorhabditis elegans, pp. 201-212 Xu et al. developed a high throughput approach for constructing genetic maps using single sperm cells. The method combines fluorescenceactivated cell sorting, whole-genome amplification, short-read sequencing, and a computational algorithm for analyzing single sperm whole-genome sequencing data. These methods allowed the authors to rapidly build a male-specific genetic map for the freshwater microcrustacean Daphnia pulex, which shows significant improvements compared to a previous map. The approach holds great promise for the study of recombination rate variation in many organisms.