What is the difference between a shire and Clydesdale?

Shires were used to develop Clydesdales, so they are similar, but Shires tend to be heavier bodied, and stand taller on average. Clydesdales also have a strong overo/sabino gene, often leaving large amounts of body white. Shires posses a grey gene, which Clydes do not (all clydes are bay, or black, with a very rare brown).