A gene is considered essential when its loss of function results in a deleterious phenotype, hugely reducing the organism's viability or fitness. However, the link between the essentiality of a gene and its degree of polymorphism is unclear. In this review, we show that there is a place for a certain degree of variability, even for essential genes.We first study the role of infectious diseases in the prevalence of genetic disorders among humans: balancing selection has selected harmful variants due to the selective pressure of pathogens because the heterozygous carrier can resist them. Then we show that the environment can induce adaptation of species by rapidly evolving genes.We also study the role of positive selection on speciation, particularly upon genes of the immune, reproductive and nervous systems. Finally, we highlight the role of regulatory sequences in changes in morphology between species and adaptation to the environment within species.

Background: Despite similar levels of coronary occlusion and standard of care management, the occurrence of scarring over adaptive heart repair following acute myocardial infarction (AMI) remains unpredictable. Recent studies indicate that mechanical cues may modulate the transcriptional programs involved in tissue repair, possibly explaining why ventricular mechanical dyssynchrony an independent predictor of post-infarction outcome. Objective: Our study aimed to investigate the relationship between mechanical cues and the outcome of post-myocardial infarction heart remodeling by live imaging. Specifically, we examined the impact of individual variability of myocardial dyssynchrony, characterized by a divergent direction of injured left ventricle wall movement next to live tissue, on the formation of a large scar, dilation of the left ventricle, and loss of pumping function. Methods: We assessed the location and degree of regional systolic and diastolic dyssynchrony using transthoracic echocardiography coupled with speckle tracking imaging. Specifically, we measured the difference in absolute strain values between adjacent regions of the left ventricle at 5 days following the induction of a standard experimental infarction in female C57Bl6 mice. Three weeks later, transthoracic echocardiography was repeated to analyze the mass and global function of the left ventricle right before termination. We then examined the size of the scar in matched mid-sections of the left ventricle circumferential segments from each mouse using histomorphometry. Finally, we evaluated the potential impact on transcriptional tissue repair programs using spatial transcriptomic analysis on representative hearts with either adaptive or fibrotic post-infarction heart remodeling. Results: We analyzed all 96 systolic and diastolic strain-related parameters in the same 48 regions of the left ventricle in all mice, with echocardiographic and histological sections following the same orientation. Stepwise analysis of the live imaging data revealed that a combination of 8 regional strain parameters could predict fibrotic remodeling (Area under the ROC curve= 0.8290). We observed that scarring remodeling was associated with opposing trends of systolic and diastolic circumferential strain % delta values on adjacent regions at day 5, while adaptive remodeling at day 28 occurred when the trend followed the direction of control (sham) hearts. Cluster analysis of gene transcripts and speckle tracking assessment on representative hearts with adaptive or fibrotic post-infarction remodeling indicated a correlation between regional post-infarction dyssynchrony and the transcriptional program. Adrenergic receptors, including Adra1, Trpc3, and Myh7, were found to be linked to specific regional dyssynchrony values and scarring remodeling. Conclusion: Our study demonstrates the potential of regional strain parameters obtained through live imaging in predicting fibrotic remodeling following myocardial infarction. Furthermore, our findings suggest a link between regional post-infarction dyssynchrony and the transcriptional program. These results highlight the potential applicability of our approach in clinical settings and provide insights for future personalization of therapeutic strategies.