What causes lactose intolerance?

With warmer weather rolling in, many of you are probably dreaming of a nice cold ice cream cone, but not everyone can enjoy this tasty treat! In this episode, we discuss lactose intolerance - we've all heard of the unfortunate symptoms, but what are the biological and genetic causes behind this phenomenon?

Sources: 

Lactose intolerance facts: https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance

https://ghr.nlm.nih.gov/condition/lactose-intolerance#genes

https://www.theweek.co.uk/64017/lactose-intolerant-why-most-of-us-can-t-digest-milk

Lactose genetics: http://www.vivo.colostate.edu/hbooks/pathphys/digestion/smallgut/lactose_intol.html