1 1a
Eggs are coaxed to mature in a culture dish. Each has a remnant egg cell called the polar body and cumulus cells from the ovary clinging to it.
2 2a
While an egg is held still with a pipette, a needle is used to drill through the zona pellucida, removing a plug.
3 3a
After ejecting the zona plug, the needle is inserted back in the egg through the hole to withdraw and discard the polar body and the egg's genetic material.
4 4a
A cumulus cell from another egg is taken up into the needle. Cells called fibroblasts (or their nuclei) can also be used in this step.
5 5a
The cumulus cell is injected deep into the egg that has been stripped of its genetic material.
6 1b
The injected egg is exposed to a mixture of chemicals and growth factors designed to activate it to divide.
7 2b
After roughly 24 hours, the activated egg begins dividing. The cells contain genetic material only from the injected cumulus cell.
8 3b
By the fourth or fifth day, a hollow ball of roughly 100 cells has formed. It holds a clump of cells called the inner cell mass that contains stem cells.
9 4b
The blastocyst is broken open, and the inner cell mass is grown in a culture dish to yield stem cells.
10 5b
The stem cells, in turn, can be coaxed to grow into a variety of cells that might one day be injected into patients.


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