Snap peas are the result of crossing Shelling peas and Snow peas and then selecting for varieties that have tender edible pods. These are all open pollinated or heirloom varieties and are all stable lines. The crossing was used to create these varieties and they will breed true.
Snap peas are a dual purpose pea that can be eaten whole, pod and all. They can also be used as a shelling pea, so if you miss them on the plant, they can be harvested and processed with your shelling pea crop.