Evolution of sex determination mechanisms and sex chromosomes

Abstract

The evolution of sex determination mechanisms and sex chromosomes has always been a central research topic in evolutionary biology. Because the sex determination process occurs during the early stage of development, and the regulation of sex-linked genes often involves non-coding RNAs and epigenetic modifications, this topic is an interdisciplinary hotspot with developmental biology and molecular biology. This review elaborates on the importance and origin of sex, numerous ways of sex determination, and the mechanisms of sex chromosome evolution. We will summarize the reported sex-determining genes and introduce the population genetic models under which the sex chromosomes evolve without homologous recombination. To date, only a few sex-determining genes have been discovered, but they have already exhibited a great diversity beyond biologists’ expectation. Future research directions will focus on identifying more upstream sex-determining genes for plants and animals and their downstream sex-determining pathways. New genome research and gene knockout techniques will develop other appropriate model organisms in this area, and to ultimately address the basic biological questions that why different organisms need to evolve such a great variety of sex-determining ways and how they transit to each other.