I'm being particularly thick, tonight, I'm afraid. When you say MC1 wakes up, do you mean MC2? Hasn't MC1 - at least his body - died? (I'm not sure when, as there is a 20 year gap between the first and second sections, but I'm sure you've got that covered.)
As I'm understanding it, MC1 has an interesting life, is fatally wounded and thanks to his genetic survival stuff, momemts before actual death manages to infiltrate his personality, but not his memory, into MC2 who happens to be on the scene. MC2's own personality is overwhelmed, so that in some sense he becomes MC1 albeit in MC2's body and with no knowledge of MC1. MC2 then leads his own exciting life. In due course he is fatally wounded and the same thing happens, this time MC3 being the victim who is taken over. That how you see it?
Writing wise, I can see a few issues.
1. Unless you start section 2 at the very point of or just after the personality transfer, you will have to show some of MC2's original voice/character. Ditto at the beginning of section 3. If you can do this for a page or two, why can't you continue it?
2. How will you show the transfer? Since MC1's memories have gone, and (presumably) MC2 never knew what MC1 was planning, neither of them is aware of what has happened.
3. If you have a later deduction eg "it must have been the Genetic Escape System in operation" you'll have to repeat it in section 3 as MC3 won't remember anything either.
4. If MC2's personality is taken over by MC1, presumably the same happens for MC3. So how are you proposing to have the backchat between the three of them, with one becoming dominant etc - or has this idea now been shelved?
5. If at the end of this, we have the same personality albeit having travelled through 3 different bodies, what is the story? Sorry, not explaining this very well. It's just I thought the 3 strands of the narrative came together in section 4, but what is the point of your writing about the GES if MC1 can't remember anything of his previous lives and he can't interact with MC2 and 3? You might as well have 3 discrete characters for all the importance the mind-merging has in that situation.
6. If you decide memory can be transferred, and/or that MC2&3 retain personality, so you have a point to section 4, then you will still need to differentiate between the 3 men in some way.
I realise I may well have got the wrong end of the stick, so just ignore my ramblings if they don't make sense. Anyway, I can't help you with the sciencey stuff I'm afraid, but I've got some questions which might help direct your thinking (or might just confuse you!):
* why 'genetic escape system' - what genes are transferred?
* what advantage is there for MC1 for this technique to have evolved/been developed?
* since there is a distinct disadvantage for the 'victim' of the GES, why has the technique been permitted?
* why not transfer of memory as well as personality?
* if MC1's memory is not transferred, does he think of himself as MC2?
* if MC2's memory is intact, surely he would realise his character had changed as he would know how he used to behave?
* does MC2's body have the GES mechanism, or is this part of MC1's personality in some way?
* when MC2 uses the GES, he is in effect doing it on behalf of MC1 since MC2's own personality has been lost, and his memories will not be carried over. If it's his own GES, how is this an advantage to MC2? (I appreciate he doesn't know he is 'really' MC1, but I still find it odd.)
* if MC3 is taken over, presumably it is by MC1, who now has no memory of being MC1 or MC2?
Hope some of this helps.