## 4 Discussion
Therefore, there is strong evidence of sex chromosomes modulating behavior responses, suggesting the importance of including polymorphisms located on the sex chromosome in genomic analyses. Animal reaction is mainly controlled by complex neural networks, which results in physiological alterations. Many pathways associated with synaptic transmission and neuroreceptor were found in our study. A specific term involved in neural networks and brain function is apoptosis. Apoptosis is one of the controlling mechanisms of the neural pool and synaptic matching between neurons during the development of the nervous system [133]. [PERSON] and [PERSON] [133] have described genes affecting the brain processes in mice (i.e., neural-apoptosis), in which _KCNK9_ gene was included. Potassium two pore domain channel subfamily-K member-9 gene (_KCNK9_) plays a role in mediating neuronal excitability [134], promoting apoptosis in granule cells [135], and encoding a protein that affects aldosterone secretion [136]. Interesting, the _KCNK9_ gene is a causal mutation in humans associated with Birk-Barel mental retardation dysmorphism syndrome, a rare maternally inherited disease (Table S9 and [137]). One of the domestication theories observes the reduction of neural crest-derived tissues due to selection for behavior [4]. Neural crest cells are stem cells that first appear during the early embryogenesis stage at the neural tube, eventually migrating ventrally throughout the body in both the cranium and the trunk [4]. In this context, the post-embryonic development term was identified in our study, which includes the _SLC18A2_ gene. Specifically, _SLC18A2_ (associated in cattle; gene from solute carrier family) plays a role in chemical synaptic transmission, locomotive behavior, and dopaminergic and serotonergic synapses. In total, 14 genes from the solute carrier family were annotated in this study (seven in cattle associated with temperament, pen score, milking speed, and rank order in herd [48; 53; 54; 55]; seven in pigs associated with feeding behavior, frequency of struggling bouts, and social genetic effect [45; 46; 47]), and they were reported in behavior-related pathways, such as long-term synaptic potentiation and depression. Out of those genes from _SCL_ family, 12 genes (12/14) and 4 genes (including _SLC18A2_) were statistically and causally associated, respectively, with human behavioral disorders. Furthermore, five genes presented a power of [PERSON]'s exact test for the allele frequency between more docile and more temperamental breed groups higher than 80% (Table S10B). Therefore, similar to observed in humans for neurodegenerative disorders [138], we suggest that genes from the solute carrier family might play an important role in behavioral traits. Behavioral responses are induced by external or internal stimuli (e.g., animal interaction, human handling, temperature alterations, and transportation). Pathways related to olfactory mechanisms were identified (Tables S4, S6, and S7). Genes from olfactory receptor family (_OR_; e.g., _OR2B6_ and _OR51E2_) were predominantly reported in those terms. Olfactory pathways were related to receptors and sensory transduction. Unknown individuals introduced to pigs stimulate new olfactory pathways, oftentimes contributing to aggressive behavior [139]. Olfactory signaling is a cue used for social recognition [139] in addition to evoking reproductive behaviors in mammalian livestock species [140; 141]. Another example of physiological alteration in response to behavior is blood pressure. Two neuropeptides out of many factors affecting the blood pressure are oxytocin and arginine vasopressin, which are well known for their roles in reproduction and homeostatic processes [142]. These molecules were also associated with the animal defensive behavior (social learning and behavior) [142; 143].