Causes of Diabetes- Genetics (Heredity)

A reference to the familial nature of diabetes can be found in ancient medical texts too. Of the total diabetics, more than 46 per cent give a family history of the disease.
There are varied opinions about how parents pass on this disease to their children. But none has been able to fully explain how heredity actually acts.
Till recent past, it was believed that the hereditary character of diabetes follows the principles of renowned geneticist Mendell, i.e.,
(1) If both the parents are diabetics, all their children get the disease,
(2) If one of the parents is a diabetic and another is a diabetes-carrier (one who does not have the disease, but can transmit it), half the number of their children get the disease,
(3) If both the parents are diabetes-carriers, one fourth the number of their children get the disease and
(4) If one of the parent is a diabetic and other is healthy, their children remain free from diabetes.
Some researchers believe that diabetes develops not because the person has inherited defective chromosome from his parents but because he has not received that chromosome from his parents, which imparts resistance to this disease.
In short, it can be said that even though hereditary factors do play a role in the development of diabetes, to what extent and in what way these factors act is still a mystery.
It can be said that hereditary factors can become effective only when certain other exciting environmental factors like obesity, faulty dietary habits and inadequate physical exertion are at work