Franz Josef Kallmann studied the biological and genetic factors of psychological disorders in Germany and the United States in the twentieth century. His studies at the New York State Psychiatric Institute in New York City, New York, focused on the genetic factors that cause psychiatric disorders. Kallmann was one of the first to use twins to study how a mental disorder is passed on by comparing the occurrence of epilepsy and schizophrenia in both fraternal and identical twins. Kallmann helped to develop and popularize the methodology of twin studies to examine the genetic component of psychiatric disorders and he showed a factor for the psychiatric disease schizophrenia.
In 1993, Dean H. Hamer and colleagues in the US published results from their research that indicated that men with speicifc genes were more likely to be homosexual than were men without those genes. The study hypothesized that some X chromosomes contain a gene, Xq28, that increases the likelihood of an individual to be homosexual. Prior to those results, researchers had argued that the cause of homosexuality was environmental and that homosexuality could be altered or reversed. Hamer’s research suggested a possible genetic cause of homosexuality. The study inspired further research into biological mechanisms of homosexuality.
Franz Josef Kallmann alichunguza mambo ya kibiolojia na ya urithi ya matatizo ya kisaikolojia nchini Ujerumani na Marekani katika karne ya ishirini. Katika utafiti wake katika Taasisi ya Psychiatric ya Jimbo la New York, New York, alizingatia sababu za maumbile zinazosababisha matatizo ya akili. Kallmann alikuwa mmoja wa wa kwanza kutumia mapacha kujifunza jinsi ugonjwa wa akili unapitishwa kwa kulinganisha kutokea kwa kifafa na schizophrenia katika mapacha wa ndugu na sawa. Kallmann alisaidia kuendeleza na kueneza mbinu ya masomo ya mapacha kuchunguza sehemu ya maumbile ya matatizo ya akili na alionyesha sababu ya ugonjwa wa akili schizophrenia. Mwaka 1993, Dean H. Hamer na wenzake nchini Marekani walichapisha matokeo ya utafiti wao ambao ulionyesha kwamba wanaume wenye jeni spesifc walikuwa na uwezekano mkubwa zaidi wa kuwa mashoga kuliko wanaume wasio na jeni hilo. Utafiti huo ulionyesha kwamba baadhi ya kromosomu za X zina jeni XQ28 ambayo huongeza uwezekano wa mtu kuwa shoga. Kabla ya matokeo hayo, watafiti walikuwa wamesema kwamba kisababishi cha ugoni-jinsia-moja kilikuwa mazingira na kwamba ugoni-jinsia-moja ungeweza kubadilishwa au kubadilishwa. Utafiti wa Hamer ulidokeza uwezekano wa kuwa na kisababishi cha urithi cha ugoni-jinsia-moja. Utafiti huo ulichochea utafiti zaidi juu ya utaratibu wa kibiolojia wa ugoni-jinsia-moja.