Monozygotic twins share approximately what percentage of their DNA?

Monozygotic twins share approximately what percentage of their DNA?

• A. 100%
• B. 50%
• C. 0%
• D. 25%

Answer: (A)

Identical twins come from a single fertilized egg that splits early in development, so they inherit essentially the same genetic material. Because the same DNA is shared by both embryos, they have about 100% of their DNA in common. The other options don’t fit that biology: 50% is what you’d expect for regular siblings or fraternal twins, 0% would mean no shared genes, which isn’t possible for twins from one zygote, and 25% would resemble the level of sharing seen in half-siblings. In reality, there can be tiny differences due to post-zygotic mutations or epigenetic changes, but the baseline genetic overlap is effectively complete.

Identical twins come from a single fertilized egg that splits early in development, so they inherit essentially the same genetic material. Because the same DNA is shared by both embryos, they have about 100% of their DNA in common. The other options don’t fit that biology: 50% is what you’d expect for regular siblings or fraternal twins, 0% would mean no shared genes, which isn’t possible for twins from one zygote, and 25% would resemble the level of sharing seen in half-siblings. In reality, there can be tiny differences due to post-zygotic mutations or epigenetic changes, but the baseline genetic overlap is effectively complete.