As both blood type and Rh factor are genetically inherited traits controlled by alleles located on chromosome 9 and chromosome 1 respectively, the study indicates a potential link between genes on autosomes and homosexuality.The biology of sexual orientation has been studied in detail in several animal model systems.In another finding, thirty-three of the forty sibling pairs tested were found to have similar alleles in the distal region of Xq28, which was significantly higher than the expected rates of 50% for fraternal brothers. With the larger sample set and complete genome scan, the study found somewhat reduced linkage for Xq28 than reported by Hamer et al.This was popularly dubbed the "gay gene" in the media, causing significant controversy. in 1998 reported on their similar study, in which they found that 13% of uncles of gay brothers on the maternal side were homosexual, compared with 6% on the paternal side. (2005) performed a full-genome scan (instead of just an X chromosome scan) on individuals and families previously reported on in Hamer et al. However, they did find other markers with a likelihood score falling just short of significance at 7q36 and likelihood scores approaching significance at 8p12 and 10q26.Monoamniotic twins share a hormonal environment, but can suffer from the 'twin to twin transfusion syndrome' in which one twin is "relatively stuffed with blood and the other exsanguinated".Chromosome linkage studies of sexual orientation have indicated the presence of multiple contributing genetic factors throughout the genome.'MZ' indicates identical twins with the same sets of genes and 'DZ' indicates fraternal twins where genes are mixed to an extent similar to that of non-twin siblings.In a study of 61 pairs of twins, researchers found among their mostly male subjects a concordance rate for homosexuality of 66% among monozygotic twins and a 30% one among dizygotic twins.
In mammals, a group of geneticists at the Korea Advanced Institute of Science and Technology altered the sexual preferences of female mice by removing a single gene linked to reproductive behavior.
The study population included 409 independent pairs of gay brothers, who were analyzed with over 300,000 single-nucleotide polymorphism markers.
The data strongly replicated Hamer's Xq28 findings as determined by both two-point and multipoint (MERLIN) LOD score mapping.
10q26 showed highly significant maternal loading, thus further supporting the previous family studies.
Results from the first large, comprehensive multi-center genetic linkage study of male sexual orientation were reported by an independent group of researchers at the American Society of Human Genetics in 2012.