Final answer:
Murray Barr was the scientist who first discovered the darkly staining bodies in nuclei of cells from female cats, which were later shown to be the inactive X chromosomes.
Step-by-step explanation:
The scientist who first discovered darkly staining bodies in nuclei of cells from female cats which were later shown to be the inactive X chromosomes was Murray Barr. He made this discovery in 1949, and the structures became known as Barr bodies in his honor. They are used to determine the presence of inactive X chromosomes in female cells.