What is a common characteristic of fraternal twins?

Fraternal twins, also known as dizygotic twins, arise from two separate eggs fertilized by two separate sperm cells during the same pregnancy. This allows for each twin to have a unique set of genes, which contributes to the possibility that they may or may not look alike. Unlike identical twins, who develop from a single fertilized egg that splits into two embryos and share identical DNA, fraternal twins can exhibit a range of physical similarities or differences.

The genetic diversity of fraternal twins means that they can be of different sexes, come from different genetic backgrounds, and have varied physical characteristics such as hair color, eye color, and even height. This variability is a defining characteristic that distinguishes fraternal twins from identical twins, who look more alike due to their identical genetic makeup.

In contrast, sharing a placenta (as seen in some identical twin pregnancies) or always being of the same sex does not apply to fraternal twins, as they typically have separate placentas and can be male, female, or a combination thereof. Therefore, the characteristic that fraternal twins may or may not look alike is a key distinguishing factor.