Because genes occur in pairs in body cells, one gene of a pair may have one effect and another gene of that same pair (allele) may have a 
(genes; occur; L:in pairs in body cells) (one gene of a pair; may have; one effect) (another gene of that same pair; may have; a)
genes one gene of a pair another gene of that same pair
occur may have may have
L:in pairs in body cells
one effect
a