Doctors confirm new type of twin born from one egg and two s
Doctors in Australia say they have identified a second case of twins apparently created from one egg and two sperm, a boy-girl combination in whom the mother’s DNA is identical in both babies but the father’s DNA varies in each twin.

They’re being called semi-identical twins and a new study in the New England Journal of Medicine suggests that such twins are extraordinarily rare. The only other reported case was uncovered in 2007.

Virtually all twins are either fraternal (where two eggs and two sperm have created two separate embryos) or identical (where one embryo splits in two before resuming normal development for each child).

“This is confirming there is this third type of twinning where it’s not fraternal and it’s not identical. It’s this strange place in between,” chief author Dr. Michael Terrence Gabbett of Queensland University of Technology in Brisbane told Reuters Health in a telephone interview.

Each sperm cell contains half the father’s DNA. But it’s not identical from sperm to sperm because each man is a mixture of the genetic material from his parents, and each time a slightly different assortment of that full DNA set gets divided to go into a sperm.

For example, some sperm will contain a copy of the father’s Y chromosome that makes the child develop into a boy and some will carry the father’s X chromosome, which makes the child a girl.

In the case of the Australian twins, who live in Brisbane and are now 4-and-a-half years old, the mother’s egg was fertilized with one sperm carrying an X chromosome and one with a Y. Because an ultrasound taken early in the pregnancy showed that both fetuses shared the same placenta, doctors assumed the fetuses were identical twins.

Read more: https://thewire.in/health/doctors-confirm-semi-identical-twins-born-from-one-egg-and-two-sperm
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