g ., ▁model ing ▁such ▁human ▁dise ases ▁as ▁Park inson ' s , ▁ne op las ia , ▁ob es ity , ▁and ▁di ab etes . ▁ ▁V ision ▁▁ ▁The ▁comp ound ▁eye ▁of ▁the ▁fruit ▁fly ▁contains ▁ 7 6 0 ▁unit ▁eyes ▁or ▁om mat idia , ▁and ▁are ▁one ▁of ▁the ▁most ▁advanced ▁among ▁insect s . ▁Each ▁om mat id ium ▁contains ▁eight ▁phot ore ceptor ▁cells ▁( R 1 - 8 ), ▁support ▁cells , ▁p ig ment ▁cells , ▁and ▁a ▁cor nea . ▁Wild - type ▁f lies ▁have ▁re dd ish ▁p ig ment ▁cells , ▁which ▁serve ▁to ▁abs orb ▁excess ▁blue ▁light ▁so ▁the ▁fly ▁is ▁not ▁blind ed ▁by ▁ambient ▁light . ▁ ▁Each ▁phot ore ceptor ▁cell ▁consists ▁of ▁two ▁main ▁sections , ▁the ▁cell ▁body ▁and ▁the ▁r hab dom ere . ▁The ▁cell ▁body ▁contains ▁the ▁nucle us , ▁while ▁the ▁ 1 0 0 - μ m - long ▁r hab dom ere ▁is ▁made ▁up ▁of ▁to oth br ush - like ▁stack s ▁of ▁memb rane ▁called ▁micro v illi . ▁Each ▁micro v ill us ▁is ▁ 1 – 2 ▁ μ m ▁in ▁length ▁and ▁about ▁ 6 0 ▁n m ▁in ▁diameter . ▁The ▁memb rane ▁of ▁the ▁r hab dom ere ▁is ▁pack ed ▁with ▁about ▁ 1 0 0 ▁million ▁rh od ops in ▁mole cules , ▁the ▁visual ▁protein ▁that ▁absor bs ▁light . ▁The ▁rest ▁of