Female-biased gene expression. (a) The sex of samples can be pre-identified by PKCIW-based PCR genotyping. A PCR product of 500 bp indicates female genotype. F, Female, M, Male. (b) and (c) PKCIW is expressed in the female but not in the male at HH4 (b) and HH15 (c). In the male embryo (c), the staining in neural tube cavity is non-specific.