Add spaces: ButtheMAINfactorgoverningvariationsbetweenpeopleisgeneEXPRESSION.

Answer: But the MAIN factor governing variations between people is gene EXPRESSION.

Add spaces: 6.Zig-zagthecornerinside.

Answer: 6. Zig-zag the corner inside.

Add spaces: Anditgoesthroughthevariableconfigurationoftheinnerside.

Answer:
And it goes through the variable configuration of the inner side.