There’s a minor Star Wars legends character named Alpha-Ø2 aka Spar aka Mandalore the Resurrector and for those of you who don’t know this clone trooper inherited Jango Fett’s genetic memory.
To quote Wookiepedia “when he was biologically seventeen years of age, Alpha-Ø2 heard a mention of Jango Fett's exploits, which triggered a memory in him—not of his own life, but of Fett's”
I have a million questions starting with why this clone trooper and ending with how does that work.
As far as I’m aware genetic memory — especially the way it presents in Spar — is entirely theoretical. Especially in humans. Instincts are one thing but remembering someone else life because of shared DNA? Nah.
But Star Wars is sci fi so let’s assume there are species in the galaxy far, far away who pass memories to their genetic offspring. 
Here’s where we get into theory/head canon space.
Let’s assume Jango Fett isn’t fully human (I know that idea isn’t novel, I’ve seen this fandom’s smut). Let’s assume some of his not-fully human DNA comes from an ancestor belonging to a species who have genetic memory. Now Jango doesn’t have his parents memories and neither does Arla but it’s a possibility — with the right circumstances, the right genetic manipulations it’s not impossible.
I don’t think Dooku or Jango knew about the chance for genetic memory until Kamino but upon starting the project the Kaminoans went ‘hey did you know you have the genetic possibility to have memories encoded into your DNA?’
There’s a lot of possibilities in this quirk. Imagine an army born already knowing how to aim a blaster, how to swim or throw a punch. But there’s a risk — who knows what genome controls Jango’s ability to pass on what memories. What if in trying to give the clones genetic memory of swimming they also give them Jango’s memories of learning to swim.
This is firmly headcanon/AU territory but I think to the Kaminoans that reward would outweigh the risk. Plus as self proclaimed “masters of genetics” that challenge — to engineer memories of skills but not moments — would be tempting. If sometimes a clone or two had more than Jango’s skills but his memories… well that’s what reconditioning is for.
Spar is not the only clone to inherit Jango Fett’s memories. He’s just the only one who survived.
