Sexual Reproduction for Same Sex Couples?

The Chromosome Chronicles

One of the common arguments against gay marriage goes something like this: marriage is an institution that is meant to support reproduction, and same-sex couples can’t sexually reproduce. Full disclosure: I support gay marriage. However, regardless of my opinion, this entry will help debunk this specific argument. More importantly, I will outline three important discoveries that will one day allow same sex couples to have biological children that are purely made from their genes

The definition of sexual reproduction needs to be clarified here. According to Wikipedia, sexual reproduction passes “a combination of genetic material to offspring, resulting in diversity.” I’m going to clarify: sexual reproduction is when the DNA of the two parental units, through the process of meiosis (formation of a gamete) and the process of fertilization, each contribute to ~50% of the genes of the resulting offspring.

Now let’s go through some basic stem cell science (read: skip this paragraph if you know the basics). Stem cells are characterized by two abilities: self-renewal and potency. Self-renewal describes their ability to divide indefinitely. Potency refers to the fact that stem cells can “differentiate” into different types of specialized cells. Adult stem cells are generally “multipotent” which means they can differentiate into a few cell types. Embryonic stem cells are “pluripotent” which means they can become any type of cell in the body. This is the reason that embryonic stem cells are so interesting: pluripotency. Pluripotent stem cells are a necessity for same-sex couples to reproduce. Now that we’ve covered some basics, we’ll move on to the three important breakthroughs that will make same sex reproduction possible:

1. Cellular reprogramming: the creation of induced pluripotent stem cells (iPSCs)

One source of pluripotent stem cells is the inner cell mass of a developing embryo – embryonic stem cells. However, a technique known as “cellular reprogramming” allows a pluripotent stem cell to be created from a mature adult skin cell after being treated with a number of transcription factors. These cells have been dubbed “induced pluripotent stem cells” or iPSCs. They are nearly identical to embryonic stem cells. More importantly, they are genetically identical to the person who donated the skin cells. This makes the cells “individualized” pluripotent stem cells. These cells can be used to form any type of tissue in the body.

2. Creation of Oocytes (eggs) from pluripotent stem cells

Pluripotent stem cells can be directed to “differentiate” into any type of cell in the body. It was reported in 2003 that scientists successfully directed mouse pluripotent stem cells to differentiate into mouse oocytes. What this means is that a skin cell can be taken from any person (male included) reprogrammed into an iPSC, and then the iPSC can be differentiated into an egg cell. This is the discovery that can help two men have a child together.

3. Creation of Sperm from pluripotent stem cells

The same exact logic from eggs can be applied to sperm. Scientists have recently demonstrated the ability to form sperm from embryonic stem cells. While the team has warned that this science will not be used for fertility treatment, the creation of sperm still has ramifications beyond infertility research. For the purpose of same-sex reproduction, the creation of sperm in vitro can one day help two women have a child together.

Application of these discoveries towards same-sex reproduction:

These three techniques, once perfected will lead to the ability for male/male and female/female couples to have biological children, children who are a combination of their own genes. The creation of eggs from pluripotent stem cells is important for male/male couples, and the creation of sperm from pluripotent stem cells is important for female/female couples. Below, I will walk step-by-step through the scenarios for male/male and female/female couples.

Sexual Reproduction for Gay Couples:

For a gay couple, one man needs to be

  

designated as the father (the one who donates the sperm), and the other as the mother (the one who donates the egg). The “father” in this case can just donate sperm the normal way…no hardcore science is really involved. The “mother,” however, needs to employ the reprogramming and differentiation techniques discussed above. Specifically, this man needs to donate skin cells. These cells must be reprogrammed into iPSCs, and the iPSCs must then be differentiated into eggs (this process is shown to the right). Once the eggs are created, they can be mixed with the sperm from the “father” to create an embryo from two men.

There are a few things to be aware of. First of all, the “mother” is also responsible for donating the mitochondrial DNA, which means that the man who opts to create the egg will also be donating the mitochondrial DNA. Another issue is that men carry an X and a Y chromosome. This means that there is a 50% chance that any gametes (sperm or egg) created from a man will have a Y chromosome. The egg must not have a Y chromosome because it might result in an embryo with two Y chromosomes, which would not survive. Finally, men still cannot carry children (I’m talking about biological men (XY), despite what you may have heard in the summer of 2008), so the embryos created from the two men will have to be implanted into a surrogate mother to deliver the baby.

Sexual Reproduction for Lesbian Couples:

For lesbian couples, there are fewer

caveats to be aware of. Once again, one woman must be the “mother” by donating the egg while the other plays the role of the “father” by donating the sperm. The mother can donate the eggs just as a woman normally does through reproductive endocrinology in an in vitro fertilization setting. The “father” must utilize the reprogramming and differentiation techniques described above to produce the sperm (as summarized in the accompanying picture).

Either member of this couple is capable of carrying the embryo (or embryos). If they opt to both carry embryos at the same time, I would go so far to say that the children can be considered fraternal twins. There is one important caveat that the women must be aware of: they cannot have a son. Women only carry XX chromosomes, and neither of them are capable of donating the Y chromosome necessary for male development. For this reason, lesbian couples are only capable of having biological daughters.

Politics, Ethics, and the Like…

The application of technology towards same-sex reproduction, in my eyes, is an advancement for both gay marriage and science. Scientifically, we are learning more about child development every year, and it will allow us to bring more healthy children into the world. For same-sex couples, the once impossible concept of a biological child is now a real possibility.

While I cannot see any ethical arguments against this type of procedure, I am open to a discussion about how far this may be pushing the envelope. In any case, I am still amazed every time I think about how far we have come with the ability to help people through science.

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Induced pluripotent stem cell