In 1997, the movie Gattaca made a splash due to its extension of themes covered in “Brave New World.” It takes place in the future where most children are born through a process (not genetic engineering in the scientific sense) where the optimal combination of genes between two individuals is selected in an embryo to give birth to children that are smarter, better looking, and more athletic than the natural, or “faith born” children. The “genetically superior” are put above the faith born, and a class system emerges based on who has better genes.

Personally, I find this movie fascinating for a number of reasons. First of all, the science they describe is not very far outside the realm of current possibilities. Preimplantation Genetic Diagnosis (PGD), the process where embryos are diagnosed for chromosomal abnormalities and certain diseases, is a common practice for couples undergoing in vitro fertilization (IVF). Secondly, the movie highlights the fact that PGD is a technology that couples will want to use. Given the option, who wouldn’t try to avoid having their child carry a negative version of the ApoE gene (increasing the risk of Alzheimer’s), the BRCA gene (increasing the risk for breast cancer), or the multitude of other simple genetic diseases that are out there (cystic fibrosis, tay sachs, hemochromatosis, sickle-cell anemia, cooley’s anemia, and the list goes on).

So now we are faced with the question: could the situation described in Gattaca, where a higher class of the genetically superior exists above a lower class of the “faith born,” ever become reality? My answer is NO for a number of reasons.

First of all, the number of embryos that can be diagnosed in one round of PGD is limited by the number of eggs a woman can produce. For me, this is the most convincing argument as to why “genetically optimized” babies will never be a realistic phenomenon. Let’s look at gene selection through PGD. If we know that the mother carries a negative version of the BRCA gene (let’s assume the father does not), then there is a 50% chance (basic Mendelian inheritance) that any embryo created by these two individuals will carry a negative BRCA gene.

Okay, so given two embryos, we would expect there to be one embryo that met the requirements of not carrying a negative BRCA gene. That’s fine. Now let’s add another gene to the list. ApoE: the father carries one copy of the negative ApoE allele. Again, 50% of the embryos will carry a negative ApoE gene. But wait: we’re faced with a problem now. By combining the requirement that the embryo we want should not carry a negative BRCA nor a negative ApoE gene, we are reducing the number of embryos that fit the bill to 25%. That means that out of four embryos, statistically we would only expect one of them to be clear of both negative ApoE and BRCA genes.

Now we can see the limitations, selecting for one gene dictates that we need two embryos to choose from. Selecting for two genes dictates that we need 2² = 4 embryos to choose from, and selecting for 3 genes will require that we have at least 2³ = 8 embryos to choose from.

Due to the fact that there is an exponential increase in the number of embryos required in selecting one that has the “preferred” version of each gene, PGD is actually limited to the number of embryos that can be produced. Currently, when a couple goes in for IVF, the woman must undergo hormone therapy to stimulate the production of more eggs. According to one source, on average 5-15 eggs are retrieved with on cycle of treatment from a reproductive endocrinologist. With a limit of up to 15 embryos, it is unlikely that more than four genes can be selected together to produce a “genetically perfect” baby. If you wanted to control the inheritance of a mere 15 genetic loci, the odds of you finding an embryo that matched your requirements would be 1/(2^15), or 0.31%.

In “Gattaca”, the reproductive technologist informed the couple that all genes were optimized. There are thousands upon thousands of genes in the human genome. You have a better chance of winning the lottery than finding one out of 15 embryos that contains every preferred version of every gene from each parent. Rest assured ladies and gentlemen, you will not be seeing any perfect children for quite a while (except for your own of course).