Complex traits differ from Mendelian traits because the relationship between genotype and phenotype is not direct.
While this is very likely a good approximation for traits such as human height, it is not appropriate for hybrid sterility traits, because the Dobzhansky-Muller model predicts epistatic interactions between loci are necessary to observe hybrid defects.
Genetic discoveries based on investigation of the mouse allow insights into human traits because of the degree of conservation between the mouse and human genomes.
Genomic correlations were lower than pedigree-based genetic correlations and they were highest between general mastitis and pathogen-specific traits because of the part-whole relationship between these traits.
Additionally, several emerging adulthood facets mediated the relation between age and the Dark Triad traits; i.e., older participants were lower on the Dark Triad traits because of the successful transition through emerging adulthood.
In population genetic terms [ 16, 17], demographic transitions can influence selection because (1) the variance in fitness can constrain the covariance between traits and fitness and (2) environmental changes independently shape the covariance between traits and fitness.
The multi-trait QTL model allows the analysis of several traits simultaneously, and thus the genetic basis of the correlations between traits.
Because fixed effects in the final models varied between traits, sample sizes for final models varied and are given in the results (tables 2 and 3).
Although, simply counting numbers of QTLs may be misleading, because of correlations between traits under consideration, and possible mis-identification of multiple LOD peaks in close vicinity (5-10 cM) as separate QTLs, it is noteworthy that chromosome 19 consistently harbored a higher number of QTLs than any other chromosome (this study, BC data [ 7] and [ 16]).
Because genetic correlations exist between traits, their selection cannot be considered separately.
