The red balls are each false-color digital images of a nucleus of a fruit fly salivary gland cell. The nuclei are 50 micrometers in diameter, about one-half the width of a human hair. Each ball is composed of about 2,000 chromosome fibers. The yellow-green dots, multiple copies of a specific gene marked by green fluorescent protein (GFP), are all snuggled up together in the top image, the nucleus without condensin II. The bottom image shows how the GFP-marked genes are moved apart after condensin II is produced in the nucleus.