Can siblings look totally different?

At first it might seem like kids from the same parents should look alike. But brothers and sisters don't look exactly alike because everyone (including parents) actually has two copies of most of their genes. And these copies can be different. Parents pass one of their two copies of each of their genes to their kids.

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How different can siblings DNA be?

Because of recombination, siblings only share about 50 percent of the same DNA, on average, Dennis says. So while biological siblings have the same family tree, their genetic code might be different in at least one of the areas looked at in a given test. That's true even for fraternal twins. What birth order says about personality? Birth order does not appear to influence personality in adults, according to several ambitious studies published in the past few years. This new wave of research relied on larger data sets and more robust statistical methods than earlier reports that claimed to find a relationship between birth order and personality.

Why don't my identical twins look alike?

Identical twins came from the same sperm and egg, so they have the same chromosomes and genes. As identical twins get older they may look more and more different, because they are exposed to more diverse environments. The science of epigenetics explains how these environmental influences can affect the genes. You can also ask do identical twins look exactly the same? At first blush it might seem impossible they could look so different. After all, while huge differences can and do happen with fraternal twins, identical twins are usually exactly that -- identical in skin, hair and eye color.

How is it possible for two identical twins to be born identical but not be identical later on in life?

A boy and a girl from Brisbane, aged four, have been identified as only the second set of semi-identical, or sesquizygotic twins, in the world. They are the first to have been observed in utero (in the womb). This extremely rare phenomenon is the result of two sperm fertilising the same egg.