The widow's peak trait is a dominant single-gene trait. It typically does not skip generations, and the degree of the peak can vary. Since it is a single-gene trait, a child will display the dominant phenotype as long as one parent has the dominant gene. 8 out of 21 members of the royal family have a widow's peak. The name "widow's peak" comes from the old belief that women with that trait were destined to be widows.
The widow's peak gene is called ALX3 and is located on Chromosome 1. A widow's peak is actually a defect in this gene and that defect is then genetically passed down. Although a widows peak is a very mild defect, there is the possibility of more serious defects on the ALX3 gene. The physical abnormalities that happen as a result of a defect on this gene are always in the face, eyes, or nose. These are grouped under the general term frontonasal dysplasia. UniProt lists some of the major findings,"true ocular hypertelorism; broadening of the nasal root; median facial cleft affecting the nose and/or upper lip and palate; unilateral or bilateral clefting of the alae nasi; lack of formation of the nasal tip; anterior cranium bifidum occultum; a V-shaped or widow's peak frontal hairline". Although you may not be familiar with some of these terms, you definitely would be able to recognize them if you saw them. Ocular hypertelorism is an excessive spacing (hypertelorism) between the eyes (ocular), broadening of the nasal root would make a nose seem unusually wide and odd looking and median facial cleft is a cleft palate. If someone married into the Royal Family with one of these defects in their genes, they could then pass any of them onto their offspring. It is unlikely that any future offspring will develop further defects in this gene because they have such a low amount of people with widow's peaks in the family already.
Attached vs. detached earlobes are another single-gene trait. Detached earlobes are dominant, and 13 out of 21 members of the royal family have attached earlobes.
Brown eyes are generally dominant over other colors, but eye color is a complex trait that involves several genes. Two parents with the same color eyes will not necessarily have a child with the same color eyes. However, the vast majority of the members of the royal family have blue eyes, besides only Kate Middleton with green eyes, Princess Beatrice and Princess Eugenie with hazel eyes, and Mark Phillips with brown eyes.
Not much is known about the genetics behind male pattern baldness. Since it's a common condition that 50% of men in their 50s suffer from, researchers have discovered that it's not important whether or not men go bald, but at what age they start balding. They have also discovered that the gene connected to balding is found on the x chromosome, meaning male pattern baldness is inherited from the mother's side. Several men in the royal family began suffering from baldness, known "the curse of the Windsors" at an early age: