Guide Dog DNA; Blind Mountain Biker

3,000 puppies are to have their DNA sequenced via sailva swabs in order to build a database that will help improve the success rate of fully established working guide dogs. The 'Born to Guide' project is being led by Dr Tom Lewis, who told us how the database will establish links between dog genetics, health and behaviour. And we meet Xavier Hopkins - the visually impaired mountain biker who makes a mental map of the courses he rides, before hurtling down them at very high speeds.