Christmas present he was given 10 years ago – a kidney.That selfless gift from someone he had never met changed his life and has given him the chance to watch his children grow up.And Ross, 48, hopes in the future another two strangers will give the same magical gift to his sons Euan, 16, and Blair, 13.Since Ross’s transplant in 2010, both his boys have been diagnosed with the same hereditary condition – polycystic kidney disease (PKD) – which means one day they too could need a transplant.Ross,