What is the most likely mode of inheritance for the followin

What is the most likely mode of inheritance for the following pedigree and explain your reasoning:

Solution

The above pedigree follows X linked dominant mode of inheritance. This is because , in the First generation, all the 3 children are affected as the parents are affected. In the 2nd generation, when the marraige between F1 affected male to normal female affected only female as because she recieves the X chromosome from her father. The brothers of the affected female are unaffected as they receive only Y chromosome from the affected father.

When the F1 female is married to normal male, all their children are affected as their mother (F1 female) is affected.

In the 3rd generation, all the females and some males are effected. The affected male in the thrid generation might be due to penetrance.