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The DNA from mum and dad form two balls of genetic information in the embryo called pronuclei, which will fuse to create the genetic blueprint for a child.

Next, the researcher empties a fertilized donor egg of its genetic material and squirts the pronuclei into the hollow egg.

The egg nucleus, now known as the female pronucleus, and each body contain the reduced or haploid number of chromosomes.

Researchers would take a fertilized egg and remove the two pronuclei, the sperm and egg's DNA before they combine, while leaving behind any mitochondria.

In Echinus, for instance, the two pronuclei fuse, and the spindle and chromosomes are formed from the zygote nucleus, whereas in the mouse the two pronuclei retain their distinctness during the formation of the chromosomes.