What happens when some genetic material is missing?

Abnormalities. Loss of genetic material is called a deletion, if less than a whole chromosome or oartial or complete monosomy if it is a sizeable part or a complete loss of a chromosome. It often results in loss of the fetus (miscarriage) but smaller losses/deletions can result in poor growth before and after birth, congenital birth defects, delays in development, and recognizeable syndromes with anomalies.