Has recombination changed during the recent evolution of the guppy Y chromosome?

Genome sequencing and genetic mapping of molecular markers have demonstrated nearly complete Y-linkage across much of the guppy (Poecilia reticulata) XY chromosome pair. Predominant Y-linkage of factors controlling visible male-specific coloration traits also suggested that these polymorphisms are sexually antagonistic (SA). However, occasional exchanges with the X are detected, and recombination patterns also appear to differ between natural guppy populations, suggesting ongoing evolution of recombination suppression under selection created by partially sex-linked SA polymorphisms.

How did the guppy Y chromosome evolve?

The sex chromosome pairs of many species do not undergo genetic recombination, unlike the autosomes. It has been proposed that the suppressed recombination results from natural selection favouring close linkage between sex-determining genes and mutations on this chromosome with advantages in one sex, but disadvantages in the other (these are called sexually antagonistic mutations). No example of such selection leading to suppressed recombination has been described, but populations of the guppy display sexually antagonistic mutations (affecting male coloration), and would be expected to evolve suppressed recombination.

PromethION Sequencing and Assembly of the Genome of Micropoecilia picta, a Fish with a Highly Degenerated Y Chromosome.

We here describe sequencing and assembly of both the autosomes and the sex chromosome in Micropoecilia picta, the closest related species to the guppy, Poecilia reticulata. Poecilia (Micropoecilia) picta is a close outgroup for studying the guppy, an important organism for studies in evolutionary ecology and in sex chromosome evolution. The guppy XY pair (LG12) has long been studied as a test case for the importance of sexually antagonistic variants in selection for suppressed recombination between Y and X chromosomes.

Mental Health Outcomes Among British Healthcare Workers-Lessons From the First Wave of the Covid-19 Pandemic.

Objective: To ascertain the level of psychological distress, using validated psychology tools, among British National healthcare workers (HCW) during the first wave of the Covid-19 crisis.

Methods: A multi-centre, anonymized, all-comer staff survey across 3 hospitals in Lancashire, England during the Covid-19 first wave (April to June 2020), consisting of Patient Health Questionnaire (PHQ-9), Perceived Stress Scale-10 (PSS-10), Generalized Anxiety Disorder-7 (GAD-7), and Impact of Events Scale (IES-6).

Results: Among 1113 HCW, median (IQR) PHQ-9, GAD-7, PSS-10, and IES-6 score was 7 (3 to 11), 6 (3 to 11), 19 (13 to 24), and 9 (5 to 14), respectively.

Locating the Sex Determining Region of Linkage Group 12 of Guppy ().

Despite over 100 years of study, the location of the fully sex-linked region of the guppy () carrying the male-determining locus, and the regions where the XY pair recombine, remain unclear. Previous population genomics studies to determine these regions used small samples from recently bottlenecked captive populations, which increase the false positive rate of associations between individuals' sexes and SNPs. Using new data from multiple natural populations, we show that a recently proposed candidate for this species' male-determining gene is probably not completely sex-linked, leaving the maleness factor still unidentified.

Using GC Content to Compare Recombination Patterns on the Sex Chromosomes and Autosomes of the Guppy, Poecilia reticulata, and Its Close Outgroup Species.

Genetic and physical mapping of the guppy (Poecilia reticulata) have shown that recombination patterns differ greatly between males and females. Crossover events occur evenly across the chromosomes in females, but in male meiosis they are restricted to the tip furthest from the centromere of each chromosome, creating very high recombination rates per megabase, as in pseudoautosomal regions of mammalian sex chromosomes. We used GC content to indirectly infer recombination patterns on guppy chromosomes, based on evidence that recombination is associated with GC-biased gene conversion, so that genome regions with high recombination rates should be detectable by high GC content.

Exaggerated heterochiasmy in a fish with sex-linked male coloration polymorphisms.

It is often stated that polymorphisms for mutations affecting fitness of males and females in opposite directions [sexually antagonistic (SA) polymorphisms] are the main selective force for the evolution of recombination suppression between sex chromosomes. However, empirical evidence to discriminate between different hypotheses is difficult to obtain. We report genetic mapping results in laboratory-raised families of the guppy (), a sexually dimorphic fish with SA polymorphisms for male coloration genes, mostly on the sex chromosomes.

Chemotherapy treatment and survival in older women with estrogen receptor-negative metastatic breast cancer: a population-based analysis.

Unlabelled: To investigate the survival benefit associated with chemotherapy receipt in older women with estrogen receptor-negative (ER-) Stage IV breast cancer.

Design: Observational, retrospective cohort study using Cox proportional hazards regression to determine effect of chemotherapy on hazard of all-cause mortality. The two samples were an overall sample (n=1,519) and a propensity score-matched sample (n=580) to control for selection to treatment receipt.

Prehospital triage of acute myocardial infarction: wireless transmission of electrocardiograms to the on-call cardiologist via a handheld computer.

Background: Use of intravenous fibrinolytic agents and percutaneous coronary interventions produce the greatest benefit when they are implemented in the first 2 hours after symptom onset. Further delays in the time to treatment typically lead to reduced benefits and poorer outcomes.

Methods: Cabarrus County Emergency Medical Service personnel complete an acute myocardial infarction case report form and assess a 12-lead electrocardiogram (ECG) to determine if ST elevation of at least 1 mV in at least 2 contiguous leads is present and then to transmit the ECG wirelessly to the emergency department (ED).