What if we could make viable human sperm or eggs from skin cells? How would that change who could reproduce? 

Usually, eggs and sperm are created inside the body, in a process known as gametogenesis. In vitro gametogenesis (IVG) is a technique used to create gametes outside the body. 

Here's how it works. Scientists take a regular cell — an adult skin cell, for instance, or a blood cell — and they chemically reprogram it to be similar to an embryonic stem cell. It's important that the reprogramming bestows "pluripotency" — the ability to turn into any of the body's cell types. Then, under precisely the right conditions, they coax the cell to develop into a sperm or an egg. Sperm meets egg in a petri dish, embryo is put into body, and offspring is born. 

No humans have been conceived through this technique yet. But in mice, IVG sperm and eggs have given rise to live pups.

It's not certain that the same will be possible for humans. But it's worth contemplating. We already know that human adult cells can be reprogrammed to be pluripotent. We know that they can be differentiated into rudimentary gametes. Many experts with their eye on the field believe that IVG in humans will eventually be made to work.

If they are right, conception may become a possibility for many more people — and many more combinations of people. And IVG would allow those people to pass on their genes. 

Below, seven groups that could be affected.

1. Reproductive-age hetero people with infertility

Some men just don't produce sperm. Some women just don't produce viable eggs, or they lose that capacity while they're young. This technique could render them fertile. Some people undergo cancer treatments or have accidents that take away their fertility. This technique could help them too. It's possible that much of heterosexual infertility could be overcome with IVG.

2. Same-sex couples

It takes a sperm and an egg to produce a human offspring and sperm are created in male reproductive organs and eggs in female ones. This technique changes that. In a female same-sex couple, an egg could be contributed from one partner and a sperm generated in vitro from a cell from the other partner. Both would be genetic parents of the offspring. Similarly, in a same-sex male couple, one partner could contribute the sperm and the other could contribute a cell that could be turned into an egg. In theory, any two people could have their cells turned into either of the two required gametes, which could be united in a dish to form an embryo. Those two people would be the genetic parents of the offspring. 

3. Post-menopausal women

Women who have aged out of reproduction could transform a skin cell into an egg cell, have it fertilized by a sperm and have a genetically-related child. 

4. Friends

Two people with no sexual feelings for one another could decide to conceive a child together. Two female friends, for instance, may decide that they'll use one woman's egg and turn the other's cell into sperm. They would both be genetic parents to the child. Two male friends could decide the same. (Two opposite-sex friends can do this now using IUI or IVF.)

5. Single people on their own

An individual may decide to reproduce using only their own gametes. A woman, for instance, may decide to fertilize her eggs with sperm made from her own skin cells. She could generate lots of embryos and test them, before transfer, to weed out problems caused by inbreeding. No partner needed.

6. Dead people

A woman could generate sperm from her dead husband (using cells on his old toothbrush, perhaps); a man could generate an egg from his former wife. Parents could generate gametes from children who die in accidents or war, to create grandchildren for themselves. The cells of famous, beautiful or otherwise remarkable people who are dead could be used to create highly-sought-after gametes. People may even leave legacy cells, with the hope that they will continue to reproduce after they are gone.

7. The unwitting 

We discard our cells all over the place — on pop cans and hairbrushes, into clothing and tissues, onto floors and handrails. How can we protect ourselves from genetic theft? How can we make sure we only become genetic parents when we choose to? 

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