Gene-Expression Examples

How about this picture? It is a chick embryo stained for the expression of a gene called Pitx1. It is expressed all along the hindlimb.

Perhaps you can guess that it is an important gene for the growth of hindlimbs.

A pale-colored irregular mass that is the body of a chick embryo with four developing limbs and visible vertebrate. Both hindlimbs are stained purple.
Pitx1 gene stained in a chick embryo

Or this one? This picture shows a stickleback embryo stained for the same gene. The gene is expressed where the pelvic spine forms.

It illustrates that the fish’s pelvic spine is homologous to the chick’s hindlimb and that their development shares the same gene.

A pale elongated mass that is a stickleback embryo has two small purple stained areas on the underside.
Pitx1 gene stained in a stickleback embryo