Academic journal article Genetics

The Genetics of Sex: Exploring Differences

Academic journal article Genetics

The Genetics of Sex: Exploring Differences

Article excerpt

In this commentary, Michelle Arbeitman et al., examine the topic of the Genetics of Sex as explored in this month's issues of GENETICS and G3: Genes|Genomes|Genetics.These inaugural articles are part of a joint Genetics of Sex collection (ongoing) in the GSA journals.

SEX differences affect nearly every biological process. These differences may be seen in obvious morpholog- ical traits, such as deer antlers, beetle horns, and the sex- specific color patterns of birds and butterflies. Reproductive behaviors may also be quite different between the sexes and include elaborate courtship displays, parental care of progeny, and aggressive or territorial behaviors. Beyond what meets the eye, sex differences are also pervasive in subcellular processes such as meiosis, recombination, gene expression, and dosage compensation. Sex differences are not only the domain of mul- ticellular organisms-distinct sexes are present in most single- cell eukaryotes.

The way in which sex differences evolve and contribute to biological diversity has been studied at all levels of biological organization, from molecules and cells to populations and macroevolutionary lineages. Genetic research has focused on many questions, including characterizing the regulatory hierarchies that specify sex differences during development, determining the molecular basis for the evolution of sex- specific traits, and understanding the mechanisms of dosage compensation of sex chromosomes. With the recent advent of inexpensive sequence information and other new tools, geneticists from many disciplines are able to address questions of sex-specific biology in a much wider range of organisms and gain insight into problems for which only theoretical models previously existed. The fundamental genetic differences be- tween the sexes and how they arise continue to fascinate biologists, and the results from genetic explorations of these topics are featured in an ongoing collection of articles published in GENETICS and G3: Genes|Genomes|Genetics.

The inaugural articles address some of these topics. Two studies focus on the biology of reproduction: the transition from predominantly sexual reproduction to asexuality in fungi (Solieri et al. 2014) and self-incompatibility in plants (Leducq et al. 2014). Two other articles examine differences in the evolution of sex chromosomes: Blackmon and Demuth (2014) look at the evolutionary turnover of sex chromosomes in beetles and Kirkpatrick and Guerrero (2014) use the recombining region of sex chromosomes to measure the strength of sexually antagonistic selection. Finally, two stud- ies focus on gametogenesis-sex differences in meiosis in Caenorhabditis elegans (Checchi et al. 2014) and the speci- fication and development of germinal cells in maize (Zhang et al. 2014).

Genetic Sex Determination Occurs in Different Ways with a Myriad of Outcomes

Many different genetic mechanisms of sex determination have been discovered in nature and studied deeply, using molecular-genetic tools (reviewed in Cline and Meyer 1996; Marin and Baker 1998; Zarkower 2001; Williams and Carroll 2009; Charlesworth and Mank 2010; Gamble and Zarkower 2012; Hughes and Rozen 2012). In humans, a dominant male-determining gene is present on the Y chro- mosome, whereas in Drosophila melanogaster the dose of X chromosomes is the primary determinate of sex, and in C. elegans sex is determined by the ratio of X chromosomes to autosomes. The outcomes of these pathways are also different: males and females are the result in humans and D. melanogaster vs. males and hermaphrodites in C elegans. In the yeast Saccharomyces cerevisiae (reviewed in Ni et al. 2011) diploid a/a organisms are derived by the fusion of opposite-sex, a and a haploids that are able to switch ge- netic material from one of two silent mating-type loci (HMR and HML) to the active MAT locus through gene conversion initiated by the HO endonuclease. In plants that are obligate outcrossers, self-incompatibility (SI) loci prevent productive self-fertilization, thereby effectively creating many mating types (reviewed in Barrett 2002). …

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