On each chromosome pair are smaller bodies (genes) which control all aspects of a bird, its colour, shape, bone structure, length of feather, size etc.
(On each chromosome pair; are; smaller bodies (genes) which control all aspects of a bird, its colour, shape, bone structure, length of feather, size etc.)
On each chromosome pair
are
smaller bodies (genes) which control all aspects of a bird, its colour, shape, bone structure, length of feather, size etc.