Sex Differences in Recombination in Sticklebacks.

Recombination often differs markedly between males and females. Here we present the first analysis of sex-specific recombination in Gasterosteus sticklebacks. Using whole-genome sequencing of 15 crosses between G. aculeatus and G. nipponicus, we localized 698 crossovers with a median resolution of 2.3 kb. We also used a bioinformatic approach to infer historical sex-averaged recombination patterns for both species. Recombination is greater in females than males on all chromosomes, and overall map length is 1.64 times longer in females. The locations of crossovers differ strikingly between sexes. Crossovers cluster toward chromosome ends in males, but are distributed more evenly across chromosomes in females. Suppression of recombination near the centromeres in males causes crossovers to cluster at the ends of long arms in acrocentric chromosomes, and greatly reduces crossing over on short arms. The effect of centromeres on recombination is much weaker in females. Genomic differentiation between G. aculeatus and G. nipponicus is strongly correlated with recombination rate, and patterns of differentiation along chromosomes are strongly influenced by male-specific telomere and centromere effects. We found no evidence for fine-scale correlations between recombination and local gene content in either sex. We discuss hypotheses for the origin of sexual dimorphism in recombination and its consequences for sexually antagonistic selection and sex chromosome evolution

Season 2, Episode 5: Julie

Laël Ngangmeni (\u2723, MD/PhD) and Jesse Sardell (\u2724) are joined by Sara Wang (\u2724) for a discussion on how to tell stories from a patient\u27s perspective, as well as what medical students should consider when they meet a patient for the first time. Sara Wang\u27s piece Julie was first published on The Interstitium blog. The transcript for this episode is available for download as an additional file

Season 2, Episode 3: People and Places

Dr. Hugh Silk and Jesse Sardell (\u2724) are joined by Mina Botros (\u2724) to hear about his experience meeting people -- both similar and quite different from himself -- as he got involved with vaccination efforts early in the COVID-19 pandemic. Mina Botros\u27 piece People and Places and the transcript for this episode are available for download as additional files

Season 2, Episode 2: Check Engine Light

Qiuwei Yang (\u2722) and Jesse Sardell (\u2724) are joined by pediatrician Dr. Heather Finlay-Morreale to discuss her experience of being diagnosed with a chronic illness and how that has influenced the way she cares for her own patients. Recorded April 2021. Dr. Finlay-Morreale\u27s piece Check Engine Light was first published in JAMA Neurology. The transcript for this episode is available for download as an additional file

Evolution of the canonical sex chromosomes of the guppy and its relatives

The sex chromosomes of the guppy, Poecilia reticulata, and its close relatives are of particular interest: they are much younger than the highly degenerate sex chromosomes of model systems such as humans and Drosophila melanogaster, and they carry many of the genes responsible for the males’ dramatic coloration. Over the last decade, several studies have analyzed these sex chromosomes using a variety of approaches including sequencing genomes and transcriptomes, cytology, and linkage mapping. Conflicting conclusions have emerged, in particular concerning the history of the sex chromosomes and the evolution of suppressed recombination between the X and Y. Here, we address these controversies by reviewing the evidence and reanalyzing data. We find no evidence of a nonrecombining sex-determining region or evolutionary strata in P. reticulata. Furthermore, we find that the data most strongly support the hypothesis that the sex-determining regions of 2 close relatives of the guppy, Poecilia wingei and Micropoecilia picta, evolved independently after their lineages diverged. We identify possible causes of conflicting results in previous studies and suggest best practices going forward

Heterogeneous histories of recombination suppression on stickleback sex chromosomes

How consistent are the evolutionary trajectories of sex chromosomes shortly after they form? Insights into the evolution of recombination, differentiation, and degeneration can be provided by comparing closely related species with homologous sex chromosomes. The sex chromosomes of the threespine stickleback (Gasterosteus aculeatus) and its sister species, the Japan Sea stickleback (G. nipponicus), have been well characterized. Little is known, however, about the sex chromosomes of their congener, the blackspotted stickleback (G. wheatlandi). We used pedigrees to obtain experimentally phased whole genome sequences from blackspotted stickleback X and Y chromosomes. Using multispecies gene trees and analysis of shared duplications, we demonstrate that Chromosome 19 is the ancestral sex chromosome and that its oldest stratum evolved in the common ancestor of the genus. After the blackspotted lineage diverged, its sex chromosomes experienced independent and more extensive recombination suppression, greater X–Y differentiation, and a much higher rate of Y degeneration than the other two species. These patterns may result from a smaller effective population size in the blackspotted stickleback. A recent fusion between the ancestral blackspotted stickleback Y chromosome and Chromosome 12, which produced a neo-X and neo-Y, may have been favored by the very small size of the recombining region on the ancestral sex chromosome. We identify six strata on the ancestral and neo-sex chromosomes where recombination between the X and Y ceased at different times. These results confirm that sex chromosomes can evolve large differences within and between species over short evolutionary timescales