What type of baldness have you seen?

According to Wikipidea, pattern hair loss is hair loss that primarily affects the top and front of the scalp.
In male-pattern hair loss, the hair loss often presents itself as either a receding hairline, loss of hair on the crown (vertex) of the scalp or a combination of both, while in female-pattern hair loss (FPHL), it typically presents as a thinning of the hair.

The typical pattern of male baldness begins at the hairline. The hairline gradually moves backward (recedes) and forms an “M” shape. Eventually the hair becomes finer, shorter, and thinner, and creates a U-shaped (or horseshoe) pattern of hair around the sides of the headMale pattern hair loss seems to be due to a combination of genetics and circulating androgens.
The cause in female pattern hair loss remains unclear.

Classic male-pattern hair loss begins above the temples and at the vertex (calvaria) of the scalp. As it progresses, a rim of hair at the sides and rear of the head remains. This has been referred to as a ‘Hippocratic wreath’, and rarely progresses to complete baldness. Pattern hair loss is classified as a form of non-scarring hair loss.

Female-pattern hair loss more often causes diffuse thinning without hairline recession; similar to its male counterpart, female androgenic alopecia rarely leads to total hair loss.
The Ludwig scale grades severity of female-pattern hair loss. These include Grades 1, 2, 3 of balding in women based on their scalp showing in the front due to thinning of hair.

The Ludwig Scale

The Hamilton–Norwood scale is used to classify the stages of male pattern baldness. The stages are described with a number from 1 to 7. This measurement scale was first introduced by James Hamilton in the 1950s and later revised and updated by O’Tar Norwood in the 1970s. It is sometimes referred to as the Norwood–Hamilton scale or simply the Norwood scale. The scale is regularly used by doctors to assess the severity of baldness, but it is not considered very reliable since examiners’ conclusions can vary.

According to Havard Health Publishing, Hereditary-pattern baldness starts with thinning of the hair and often progresses to complete hair loss on parts of the scalp. Hairs on the pillow, in the tub or on the comb are unreliable symptoms of hair loss. The average non-balding person loses 100 hairs per day, and more hair may fall out under certain circumstances, such as after childbirth or a serious illness.

In men, hair loss typically begins at the temples and crown and proceeds in an M-shaped pattern. In the most advanced stage, only a rim of hair along the side and back of the scalp remains.
In women, hair loss tends to be more widespread but better hidden. The top of the head down the middle is most commonly affected, often in a “Christmas tree” pattern. In contrast to men, the hairline along the forehead and temples usually remains normal in women. Complete loss of hair in any one place on the scalp is unusual and may suggest that a different problem is the cause, such as alopecia areata (an immune system disorder that causes bald patches), a fungus infection or one of a number of other skin conditions.

Prevention?
If you begin to lose hair in a hereditary pattern, you may be able to slow further hair loss by using minoxidil (Rogaine) or finasteride (Propecia). Minoxidil can be used by both men and women, while finasteride usually is used just for men.