|Strain Name||C57BL/6-F9tm1/Bcgen||Common Name||B-F9 KO mice|
||F9；FIX（coagulation factor IX）|
F9, also known as F9 p22 and FIX (coagulationfactor IX), is also located on the X chromosome like F8. It encodes a vitamin K-dependent serine protease (factor IX), which plays a key role in the intrinsic coagulation pathway. The zymogen is activated by XIa factor to obtain factor IXa, and then the inactive factor X is activated to factor Xa by the participation of factor VIIIa, calcium ions, and membrane phospholipids, and then the coagulation reaction continues. Deletion of the F9 gene leads to factor IX deficiency, which triggers coagulopathy and is hemophilia B with X-chromosome recessive inheritance, and it can be said that the F9 gene is of extraordinary significance for the study of hemophilia B.