**5. Heritable effect on human sperm structure**

The hereditary condition which causes the defects in the flagella of sperm is termed as Kartagener's syndrome, immotile cilia syndrome (ICS), or primary ciliary dyskinesia (PCD). It often leads to chronic respiratory problems, male sterility and situs inversus [19]. These states are linked directly or indirectly with the autosomal recessive traits. The aforementioned conditions make the flagella unable to show normal movement. Sperm with these syndromes have abnormal axoneme lacking dynein arm partially or completely, lack of central sheath, lack of inner arms [20]. Due to variety of defects presented in sperm and cilia, many genes are mutated and contribute to the syndrome [21]. Another flagellar defect characterized by severe asthenozoospermia is familiar as dysplasia of fibrous sheath. In this type of disorder, the sperm have disorganized and hyperplastic fibrous sheath, and very short, thick, rigid and immotile tail [17, 18]. Another flagellar defect which appears in sperm cells of infertile men is known as flagellar dyskinesia [15]. This type of defect was observed in brothers and has been suggested that it arises due to the genetic abbreviation [22]. The sperm consist of altered peri-axonemal structure but have normal axoneme. Densed individual fibers are extended abnormally along the axoneme location and number of longitudinal columns of fibrous sheath are modified and else, there are changes in the order of termination of these structures [15].
