As human evolve from a sperm and ovum the deeds which get carried during the development is DNA. This DNA get mutated during the existence of human.
He or she further mutate and share to offspring. Hence the details or information carried by a DNA stays with you which is Karma..
There is no next birth or previous birth unless you have a offspring / parent on which your part goes to them as DNA which keeps traversing forever until that line stops..
Just a thought on karma vs dna ….
Thoughts Map 