We are the result of genetic combinations. Our appearance, our propensity for certain diseases and some physical disorders are inherited from our parents and grandparents. Most genes have two or more variations called alleles. Dominant alleles can be observed, such as the cleft chin of actor Kirk Douglas. Dominance of allele doesn’t necessarily mean that a characteristic will be more frequent within a population. Even though the cleft chin is the result of a dominant allele, most people have smooth chins.
Hair, Eye and Skin Color
Hair, eye and skin color are genetically transmitted from parents to child but multiple genes are involved and the process is complicated and still not completely understood. Brunette parents can give birth to blond children. Blue-eyed parents may have green-eyed babies. Skin color is most confusing of all, especially in families with a lineage of mixed skin types. Skin color is determined by the amount of melanin it contains. The types and amount of melanin is determined by several genes. Several generations removed from an ancestor with olive skin, the child of fair skinned parents may have an olive complexion. The allele for curly hair is dominant and more than one gene may be involved in passing this characteristic on to a child. The widow's peak is the dominant allele while the straight hairline is recessive. Freckles are passed on when at least one parent has the dominant allele.
Shirley Temple’s dimples were the result of a dominant allele as was Kirk Douglas's cleft chin. Those with unattached earlobes have two parents with the same recessive alleles. Their counterparts, those with attached earlobes, need have only one parent with the dominant allele. The shape of the nose and head is also genetically determined, although more alleles are involved.
Hands and Feet
Alleles for the straight thumb and the bent pinky are dominant, while those for the bent thumb and the straight pinky are recessive. Some people have hair on the mid-digit of their fingers. This trait is the result of a dominant allele. If your second toe is longer than your big toe it was passed along through a dominant allele.
Parents with a tendency toward allergies have a 25 percent chance that their children will also have allergies. If both parents have allergies the chance goes up to 50 percent. Some traits are sex linked and carried on the X and Y chromosomes. The color blindness trait is a recessive allele carried on the X chromosome, and since women have two X chromosomes they rarely have this condition.