Final answer:
Dizygotic twins share on average about 50% of their DNA, not 25%. This is because they are just like any other siblings but born at the same time. In contrast, monozygotic twins share 100% of their DNA, as they originate from a single zygote.
Step-by-step explanation:
The claim that dizygotic twins share on average about 25% of their DNA is false. Dizygotic, or fraternal, twins are just like any other siblings except that they are born at the same time.
They share, on average, 50% of their DNA which comes from the random combination of their parents' genes during the process of meiosis.
This sharing is because each sibling gets half of their DNA from each parent, but which half is a random process due to the way our genes recombine. If twins were to only share 25%, they would be less related than typical siblings, which is not the case.
The genetics of monozygotic twins, or identical twins, is different. They originate from the division of a single zygote, which means they share virtually 100% of their DNA, making them genetically identical.
This is because the split occurs after fertilization, so all the DNA is already present and is equally divided between the twins.