Why would that be the case? If everything changes completely except the brain, wouldn't that include chromosomes?
I guess chromosomes to a lesser extent and DNA to greater would have to stay under older readings, just reshuffled...not least as it explains how Jenny matches the Doctor and ends up able to regenerate, and how things like the Rassilon Imprimatur work. Zygotes are an interesting question too, in the new paradigm, because they work differently across sexes.