Which type of twins are genetically no closer than ordinary brothers and sisters?

Fraternal twins, also known as dizygotic twins, are formed from the fertilization of two separate eggs by two separate sperm cells. This means that they share, on average, about 50% of their genetic material, similar to regular siblings who are conceived separately. Therefore, genetically, fraternal twins are no closer than ordinary brothers and sisters.

In contrast, identical twins, or monozygotic twins, arise from a single fertilized egg that splits into two embryos, resulting in them sharing 100% of their genetic information. Half-siblings share approximately 25% of their genes, while cousins share about 12.5%. This distinction is important in understanding genetic relationships, illustrating why fraternal twins are akin to ordinary siblings in genetic closeness.