Josué Barrera-Redondo

Abstract Research on the biology and evolution of sex chromosomes has primarily focused on diploid XX/XY and ZW/ZZ systems. In contrast, the rise, evolution and demise of U/V systems has remained an enigma. Here we analyse genomes of nine brown algal species with different sexual systems to determine the history of their sex determination. U/V sex chromosomes emerged between 450 and 224 million years ago, when a region containing the pivotal male-determinant MIN ceased recombining.

From the early 1970s, with the publication of Evolution by Gene Duplication by Susumu Ohno, up until the early 2000s, the prevailing view in molecular evolution was that new genes must at least partially evolve from pre-existing genes. As such, some research during this time focused on identifying the earliest existing ‘founder’ genes that were present in the last universal common ancestor.

1 Introduction Understanding how the environment influences the distribution of genetic variation is a major goal in evolutionary ecology and biogeography (Sanmartín and Ronquist 2004; Rellstab et al. 2017; Martins et al. 2018). Environmental selective pressures often vary in space and time, causing populations to evolve traits that are advantageous under local conditions (Blanquart et al. 2013; Lascoux et al. 2016; Guerrero et al. 2018).