Not fully genetics. Your skin expands so your likely to get some. You itch and they will appear more prone. Just moisture plus use bio oil during the 2nd trimester
Stretch marks are mostly genetics and if your mom got them you will most likely get them. No matter how much cream you use or how careful you are you either get them or you don't. Creams normally just help lessen the redness and the intensity of the stretch marks. Scratching may make the redness worse but hey they are just stretch marks showing that your body did an amazing thing by growing a human!