(in genetics) The doubling or repetition of part of a chromosome, which generally originates during the crossing over phase of meiosis. Occasionally this type of chromosome mutation may have beneficial effects on a population. For example, a beneficial duplication resulted in the evolution of four types of haemoglobin in humans and apes from a single form. One of these types of haemoglobin (gamma or fetal haemoglobin) has a greater affinity for oxygen and maximizes fetal uptake of oxygen from the mother’s blood.