Question 26 refers to QTL on the cricket autosomes. For the sex chromosomes, females crickets are XX and males crickets are XO, having just one X chromosome but no Y chromosome. Can QTL for pulse rate be mapped on cricket X chromosomes? If the song is only sung by male crickets, can the dominance effects of QTL on the X be estimated? GWA studies reveal statistical correlations between the genotypes at marker loci in genes and complex traits. Do GWA studies prove that allelic variation in a gene actually causes the variation in the trait? If not, what experiments could prove that allelic variants in a gene in a population are responsible for variation in a trait?