Your hamstrings are the muscles located on the back of your leg and attach at the sit bones of your hip The hamstrings consist of three muscles the semimembranosus, the semitendinosus, and the biceps femoris and are located on the back of your leg. They attach at the sit bones of your hip ((Ischial Tuberosity) and at your lower leg bone (Tibia and Fibula)
The hamstrings work to flex your knee as well as extend your hip. Put another way, they allow to bend your knee and stand tall. In the squat, our hips and knees bend and then extend. The hamstrings help stabilize the knee while descending in the squat and when we stand they shorten to “open” our hips.
There are different variations of the squat: air squat, low bar back squat, front squat and overhead squat to name a few. Studies show that the hamstring is active in all squats and it is most used in the low bar back squat.
Now if you are looking for direct hamstring work there are many different exercises such as Good Mornings, Romanian Deadlifts, Glute Ham raises
With the calves, if they were not there or “active” we would probably fall right over. The help stabilize our feet in both concentric and eccentric portions of the squat. Though they are not directly worked, they are active.
To hit up your calves directly you can work in some weighted calves raises, high jumps and sprints.
To wrap it up, your hamstrings and calves are working while squatting but if you want to give them direct attention, there are several different exercises you can execute