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While it’s a common belief that sex is determined by a single gene in humans and other animals, this notion has been challenged by claims that some species, like platyfish, require multiple genes to determine sex. To better understand these complexities, a review delved into the topic and discovered that these claims typically refer to abnormal or transitional situations, such as hybrids between two species with different sex-determining systems.
In mammals, the SRY gene on the Y chromosome acts as the “master switch” for sex determination. This system ensures a 1:1 ratio of male and female offspring. However, other vertebrates exhibit a vast array of sex-determining systems, with some species appearing to have multiple sex genes.
Aquarium fish, such as platyfish and sea bass, frogs, and lizards seem to exhibit more complex systems. The platypus, for instance, carries five X and five Y chromosomes, raising questions about sex determination in such species. These exceptional cases seem to defy the expectation of a single sex gene producing a stable system.
When examining species without an apparent single master switch gene, it’s common to refer to “polygenic sex.” However, the analysis shows that these examples often represent abnormal or transitional situations. In some cases, multiple sex genes are detected but ultimately control different steps of the same pathway regulated by a single master gene.
Transitional systems, like those seen in sea bass and European frogs, may show signs of a new system gradually replacing an old one. Moreover, hybrids between two species can reveal multiple genes with significant effects on sex determination, but in the long run, there is strong selection for one gene to dominate, resulting in a single-gene system and a 1:1 sex ratio.
Understanding these complexities in sex determination can help researchers and conservationists better manage animal populations and contribute to our knowledge of genetic diversity. We encourage readers to explore the fascinating world of sex determination and appreciate the myriad ways in which nature finds balance. By gaining a deeper understanding of these processes, we can work towards protection and maintaining biodiversity, ultimately benefiting the planet and its inhabitants.

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RED LIGHT: Understanding these complexities in sex determination can help researchers and conservationists better manage animal populations and contribute to our knowledge of genetic diversity. . . . Note the reference to “help…better manage animal populations….” WHAT ABOUT MANAGING HUMAN POPULATIONS? The species that is out of control!