University of Zagreb. Faculty of Science. Department of Biology.
Abstract
Na određivanje spola djeluju i genetički i okolišni faktori. Kod mnogih gmazova, tip gonada je determiniran inkubacijskom temperaturom jaja i taj je proces poznat kao temperaturna determinacija spola (TSD). Gmazovi sa TSD pokazuju različite odnose između temperature i omjera spolova. Niže temperature produciraju ženke, a više mužjake kod mnogih guštera i krokodila, dok je kod većine kornjača situacija obrnuta. Estrogen ima važnu ulogu u spolnoj determinaciji kod gmazova sa TSD. Neki geni uključeni u determinaciju spola kod sisavaca su ustanovljeni i u gonadama drugih kralježnjaka. Sox9, Dax1 i Dmrt1 su eksprimirani na početku razvoja gonada kod ptica i gmazova. Danas još uvijek ne znamo točno kako temperatura djeluje na spol embrija, ali se zna da važnu ulogu u tome ima estrogen. Neki toksični spojevi kao što su poliklorirani bifenili (PCBs) mogu imati djelovanje slično estrogenu i uzrokovati reproduktivne anomalije. Ovo je očiti dokaz da utjecaj čovjeka može biti štetan za okoliš i organizme u njemu.Sex determination is controlled either by genetic or environmental factors. In many reptiles, gonadal sex is determined by the incubation temperature of the egg, a process known as temperature-dependent sex determination (TSD). Reptiles with TSD exhibit various relationships between temperature and sex ratio. Low temperatures produce females and high temperatures produce males in many lizards and crocodilians, whereas this pattern is reversed in most turtles. Estrogen playes a significant role in sex determination in reptiles with TSD. Some genes of the mammalian sex-determining pathway have been identified in gonads of different vertebrates. Sox9, Dax1 and Dmrt1 are expressed at the onset of gonadal development in birds and reptiles. Today we are still unclear as to how temperature ultimately effects the sex of the embryo, but the argument for the role of estrogen appears even stronger. Some of the effects of toxicants such as polychlorinated biphenyls (PCBs) can have estrogenic effects and can induce reproductive anomalies. There is abundant evidence that manmade products can become environmental toxicants
