Yes, LINKAGE is a Scrabble word!

Letter values in Scrabble US: L 1, I 1, N 1, K 5, A 1, G 2, E 1.

Is it a valid word?

LINKAGE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

an associative relation
(genetics) traits that tend to be inherited together as a consequence of an association between their genes; all of the genes of a given chromosome are linked (where one goes they all go)
a mechanical system of rods or springs or pivots that transmits power or motion
the act of linking things together

Also: gene linkage.