**1. Introduction**

Genetics terms returns to origin from Greek genetikos meaning "genitive," which in turn derives from genesis meaning "origin" [1, 2]. Genetics in general is a branch of biology related to survey of genes, genetic variation, and even heredity in living systems [3–5]. The study of inheritance pattern that influences genes on human nature and occurs in human beings is called human genetics. Human genetics represents an original aspect that encompasses a variety of overlapping fields like the structure of gene and organization; the study of mutation detection; genetic mapping and linkage analysis; molecular diagnostics; gene expression; cytogenetics assessment; biomedical genetics; disease association studies; tumorigenesis of molecular levels; developmental genetics; and genetic epidemiology, in addition to genetics of complex disease [6, 7]. In general, genes can be considered as a key of most human inherited lesions. So, the benefit study of human genetics can be helpful to answer many questions concerning human diseases and invent effective drugs [8]. The passing of a certain genes from parents to offspring by biological process is called heredity. Each baby carries genes from their biological parents and some of these genes express particular trait or lesion [9]. Various traits may be physical like color of eyes, hair, skin, and other phenotypic matter. In other direction, some genes may play a key role in the risk of certain disorders and

increase incidence of disease, or prophylaxis from it [10]. Several disorders occur and arise from multiple factors such as genetic, lifestyle, and environmental [11]. Many previous studies revealed facts for the hereditability of main neuropsychiatric disorders, for example, depression, bipolar disorder, and schizophrenia [12, 13]. In all these behavioral disorders, a specific genetic fault is transported from parents to children and will enhance a progeny susceptibility risk of inheriting a specific disorder [11, 12, 14, 15].

Neurological and mental diseases cannot be related to genetics science alone, so it is significant to seek implicated one's genetic composition material that possibly affects various direction of human behavior [16]. The relationship between genes and behavior leads to development of highly prevalent responses and disorders throughout a new biological factors. About 30–50% of the risk for anxiety and depression is genetic, while the other 50–70% of the risk may be attributed to environmental factors, such as substance use, stress, diet, and childhood experiences [17]. A comparison between genetic and environmental factors, demonstrated about 30–50% of the risk for anxiety and depression and 50–70% of substance uses, stress, and diet, respectively [17, 18].
