Inherited Traits

Ask someone where he got his red hair from and he will likely tell you that he inherited it from one of his parents or grandparents. However, when someone says that her tendency to be messy came from a grandparent, should we assume that messiness, too, is an inherited trait? Some traits exist from birth, while others are learned from our environment. Some inherited traits remain obvious, such as eye color. But there are other more obscure inherited traits that you may never have thought about, such as a certain digit’s ability to bend.

All complex living things, plants, animals and humans contain materials that allow them to pass traits to their offspring. In the cells of all living things, genetic material resides inside the nucleus waiting to decide the traits of future generations. Genes containing DNA, one from each parent, line up on pairs of chromosomes. Hundreds or thousands of genes may exist on one chromosome. A human cell contains just 23 pairs of chromosomes but may contain up to 35,000 genes.

Prior to advances in genetic science, farmers and ranchers selectively bred plants and animals to achieve the best results. During the late 1800s, Gregor Mendel advanced theories of heredity that apply to all complex living things including humans. Experiments and advances in genetics continue today as scientists attempt to understand the science of heredity and genetics. According to Dr. Dennis O’Neil, Behavioral Sciences Department, Palomar College, San Marcos, California, Mendel focused his experiments on pea plants because they reproduced at a rate that allowed him to see two generations a year. However, today’s scientists use fruit flies that can reproduce in 2 weeks and bacteria that can reproduce in less than five hours.

The genes that determine traits have variations known as alleles. These determine slight differences in traits such as whether or not a person has dimples. Inherited alleles may be identical or different. Alleles interact in different ways. One way is to behave in a dominant and recessive manner. The dominant allele trait always presents itself when alleles differ. However, the recessive trait only presents when both alleles are recessive. This interaction only applies to traits determined by a single gene. When more than a single gene determines traits, other more complicated interactions occur.

Some common, single-gene inherited traits include chin clefts and dimples. The genes for both are dominant. Scientists disagree whether one or several gene interactions determine the trait of ear lobe attachment or detachment. Other disagreements occur among scientists regarding the tongue rolling trait, although according to a 1940 study by geneticist Alfred Sturtevant, 70 percent of those of European ancestry can roll their tongue. Hair texture, left- or right-handedness, color blindness, hitchhiker thumb, freckles, allergies and hairline shape are several other common inherited traits.

Scientists researching genes believe that altered genes may cause some illnesses and diseases. They further believe that some of these altered genes may be acquired through heredity. Currently, studies and experiments conducted in the field of genetics hope to find a way to cure such diseases as cancer. Experiments using gene therapy and genetic engineering may result in a method of using healthy genes to replace altered ones and cure illnesses.

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