However, if a man inherits one recessive copy of a gene on his X chromosome, he develops that trait because he has no additional copies of that gene. Thus, men are more likely than women to get many disorders associated with the X chromosome. Diseases that are caused by mutations on the X chromosome are called X-linked diseases. Hemophilia, a blot clotting disorder, and color blindness are X-linked disorders that are far more common in men than in women. Each cell has many mitochondria , whose job is to produce energy for the cell.
Diseases can occur if numerous copies of mitochondrial DNA within a cell have been altered.
Thus, disease genes carried on mitochondrial DNA can only be passed from mother to child. This rare pattern of inheritance is called mitochondrial DNA inheritance. Scientists believe that long ago mitochondria were actually independent bacteria. Over time, the bacteria transferred all but a small portion of their DNA over to the larger cells and were no longer able to live independently. It is thought that our mitochondria are the descendants of these bacteria and that our mitochondrial DNA is that last bit of DNA that the bacteria kept for themselves.