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      1 1 Autosomal recessive diseases develop when an individual has two copies of an abnormal gene.

      2 2 Currently, the United Kingdom is the only country that has allowed mitochondrial DNA replacement techniques. Such techniques represent the only existing method for couples where one member is affected by a mitochondrial condition to have genetically related children.

      3 3 The arguments made for CRISPR can be extended also to other future genome editing technologies. Throughout the paper, I use CRISPR and genome editing or gene editing technologies interchangeably.

      4 4 At least when it is about medical conditions, but this is the case in question, so I will not enter into a discussion on so‐called cosmetic traits and enhancement.

      5 5 This observation is conditional as it relies on the interpretation of therapy as a practice that can only be defined as such if there is a person to be treated (Rulli 2016a).

      6 6 I refer here to the debate on mitochondrial replacement techniques (MRTs) and not strictly on genome editing with CRISPR, as few commentators have dealt specifically with the question of whether genome editing is identity‐affecting (for two examples, see: Gyngell et al. 2016; Liao 2017). One of the two techniques for the replacement of faulty mitochondrial DNA, pronuclear transfer (PNT), arguably represents the most similar case to genome editing as, unlike the other technique for the replacement of mitochondrial DNA (maternal spindle transfer – MST), it is applied after the oocytes has been fertilised. The contention, in the case of PNT, is whether this technique is identity‐affecting or not, and commentators have presented differing views on this matter (Liao 2017; Palacios‐González 2017; Rulli 2016a; Wrigley et al. 2015). While I am aware that PNT and CRISPR are two distinct technologies, PNT arguably represents the most similar case to genome editing as both CRISPR and PNT are applied after fertilisation. Hence, other things being equal, arguments concerning whether PNT is identity‐affecting or not can also be considered valid in discussions on whether CRISPR is identity‐affecting. It must be noted however, that those who explicitly referred to genome editing maintained that it is not identity‐affecting (Gyngell et al. 2016; Liao 2017). Interestingly, authors who speculatively consider the possibility of using gene therapy on human embryos before the availability of CRISPR are also divided on this issue (Buchanan 1996; McMahan 2006; Sparrow 2008).

      7 7 Despite some challenges, the biological origin (or gametic origin) that a person has is widely considered a necessary condition of what determines the human being that we are. This is well explained by philosopher Derek Parfit’s ‘Origin View’ (or gametic essentialism): “each person has this necessary property: that of having grown from the particular pair of cells from which this person in fact grew” (Parfit 1984, p. 353). In other words, the fact that two gametes came together and generated me is, under this view, considered a necessary condition of my identity: I am the entity that I am by virtue of my gametic origin. Now, this is linked to the discussion of treatment and selection because a technology such as PGD is identity‐affecting. In other words, using PGD causes a numerically different person to come into being, namely a different person than the person that would have come into being had PGD not been used. In the case of genome editing, since the intervention takes place after fertilisation, the gametic origin of the genetically modified embryo and the gametic origin of the non‐genetically modified embryos are identical. In other words, these two embryos are numerically identical. The contention, however, is that gametic origin is only a necessary and not sufficient condition for having a specific identity. Thus, whether genome editing technologies applied to zygotes/embryos cause a different person to come into being or not remains an open question. If they do, then such technologies cannot be considered therapeutic because a different person comes into being due to the use of genome editing. If they do not, they can be considered therapeutic.

      8 8 If genome editing is employed before the 14th day after fertilisation (as it is required by embryos research regulations in the United Kingdom and in many other countries, Hyun et al. 2016), the embryo could still cleave into two (i.e. twinning). In this case, the children that could potentially develop from such embryo will be two. However, twinning occurs spontaneously and it is not influenced by the use of genome editing on the embryo. As a consequence, the use of the technique does not directly affect the numerical identity of the future child/children as it is not the direct causation of the embryo splitting.