The genetic basis of hair whorl, handedness, and other phenotypes.

Evidence is presented that RHD, RHCE, and other RH genes, may be interesting candidates to consider when searching for the genetic basis of hair whorl rotation (i.e., clockwise or counterclockwise), handedness (i.e., right handed, left handed or ambidextrous), speech laterality (i.e., right brained or left brained), speech dyslexia (e.g., stuttering), sexual orientation (i.e., heterosexual, homosexual, bisexual, or transsexual), schizophrenia, bipolar disorder, and autism spectrum disorder. Such evidence involves the need for a genetic model that includes maternal immunization to explain some of the empirical results reported in the literature. The complex polymorphisms present among the maternally immunizing RH genes can then be used to explain other empirical results. Easily tested hypotheses are suggested, based upon genotypic (but not phenotypic) frequencies of the RH genes. In particular, homozygous dominant individuals are expected to be less common or lacking entirely among the alternative phenotypes. If it is proven that RH genes are involved in brain architecture, it will have a profound effect upon our understanding of the development and organization of the asymmetrical vertebrate brain and may eventually lead to a better understanding of the developmental processes which occur to produce the various alternative phenotypes discussed here. In addition, if RH genes are shown to be involved in the production of these phenotypes, then the evolutionary studies can be performed to demonstrate the beneficial effect of the recessive alleles of RHD and RHCE, and why human evolution appears to be selecting for the recessive alleles even though an increase in the frequency of such alleles may imply lower average fecundity among some individuals possessing them.