The value (or lack of value) of designer babies to the human genome/evolutionWatch
What He Jiankui did was delete the CCR5 gene in the embryos (which he fertilized via IVF) because previous studies had implicated that a CCR5 deletion in mice was observed to confer a type of HIV resistance to the mice and is also suggested to enhance their cognitive function. This is, however, seen in mice and the biggest thing is that mice, although great model organisms that have been used in a plethora of ground breaking scientific research, are NOT humans. We cannot predict, simply by looking at how a CCR5 deletion in mice, how this will affect the human babies born from his experience. Up to now, there were no known instances of a germline-edited human embryos being brought to full term pregnancy (although many theorize that this is just the first case that came to the international light, but that's for a different conversation related to conspiracy theories).
The biggest thing is that we currently don't know how these babies will be affected by the deletion. If you want to keep to the "biology" of it, you could talk about how genes and the human genome function, the proposed implications genetic engineering will have the human genome, and maybe critical/important developmental genes and what happens if these are deleted (aka genetic developmental disorders related to mutations developmental genes). I'm not sure how you'd keep it 100% biology-only (I feel like you may need to address the ethics of it somewhere), but then again my essay was more ethics-focused.
The CCR5 gene and CCR5 protein functions in HIV infection could be a good start, and maybe looking into the He Jiankui 2018 controversy might give you some ideas for your research. These links might also be helpful: