Dizygote

Dizygote, also called dizygotic, is a term used in human biology to describe offspring that arise from two separate fertilizations. In twinning, dizygotic twins result when two ova are released and fertilized by two sperm, creating two zygotes that develop into two genetically distinct individuals. This is contrasted with monozygotic (identical) twins, who originate from a single zygote that splits.

Because the zygotes come from different eggs and sperm, dizygotic twins are as genetically similar as ordinary siblings, sharing on average about 50 percent of their segregating genes. They can be of the same or different sexes and usually have separate placentas and amniotic sacs, though some shared placenta or membranes can occur if the placentas fuse.

Most factors that affect dizygotic twinning include maternal age, parity, heredity, ethnicity, and the use of fertility treatments. The incidence varies widely among populations, with higher rates in some African populations and lower rates in East Asian populations. Dizygotic twinning is more common in older mothers and among women who have undergone assisted reproductive technologies, which can increase the chance of releasing more than one egg during ovulation.

In medical and genetic contexts, dizygote is used to classify a pair of offspring that originated from two separate fertilizations. The concept is a key distinction from monozygotic twinning and is central to discussions of genetic relatedness, twin studies, and prenatal development.