Correct. Increasing Pax6 expression has a negative effect on keratin 10 mRNA abundance
Effect is most commonly used as a noun, so it might be helpful, if you are ever in doubt, to remember that it will usually follow an article (the effect, an effect) or an adjective (negative effect).
In contrast, affect is most commonly used a verb, “Pax 6 affects keratin expression”
A big group of university students and a big group of lectures were in agreement that the strike was appropriate. Which phrase describes this situation?