Among the thousands of traits that humans inherit from their parents are the easily observed traits of hair color, presence of dimples and presence of freckles. Other inheritable traits include blood type and the ability to taste certain chemicals. Some inherited traits, such as height, can be modified by the environment, while others, such as blood type, cannot.
Hair color is an easily observed trait that is inherited from an individual's parents. It is determined by the presence or absence of two types of melanin: eumelanin, which causes brown and black hair, and phaelomelanin, which causes blond and red hair. Dark hair is a dominant trait, while blond hair is recessive. The presence of dimples is also inherited from parents. Having dimples is a dominant trait, while their absence is a recessive trait.
Freckles are another example of an inherited dominant trait. Parents who have freckles tend to have children with freckles. The main gene that controls the presence of freckles is called the MC1R gene. Other genes and environmental factors are responsible for modifying the intensity, number and color of freckles.
Most traits are controlled not by a single gene, but by the complex interworking of many genetic factors. Height is a good example of this phenomenon. Children with tall parents tend to be taller than those with short parents, but it is hard to pinpoint specific genes that determine height. Although some children are genetically predisposed to having certain heights because of inherited traits, environmental factors such as nutrition during childhood impact the expression of those genetic factors as well.