[js1138]

Left and right handed pairs occur in identical twins at the same rate as in the non-twin population. I was curious about the mirror image hearts, for which I found no online source.

Lots of human traits are determined by subtle environmental influences during development. Some, such as fingerprints, are completely independent of heredity.

[SoCal Pubbie]

Some sites I found said there were no known cases of mirrored internal organs, so perhaps that's not correct. Or perhaps those twins don't survive after birth.