Identical twins aren’t perfect clones, research shows

WASHINGTON (AP) — A new study shows that differences in the DNA of identical twins can show up within the first two weeks after an egg is fertilized. Scientists in Iceland studied the DNA of 387 pairs of identical twins, as well as their parents, children and spouses. They found that the average number of early genetic differences that separate identical twins is about five. But about 15% of twin pairs have a much larger number of differences, up to 100. This can influence why one twin is taller than the other — or why one twin is at greater risk for certain diseases. The work was published Thursday in the journal Nature Genetics.