Genetic Health Overview

Have you ever wondered why your eyes and hair are a certain color? Or why you grew to a certain height, and then you stopped? Our traits are determined by our genetic information, which is passed on to us from both of our parents. Every person has a unique set of genes, which is what makes us all so different. Genes play a factor in countless aspects of your physical characteristics, your personality, and your health.

DNA and Genes

Each of our cells houses a nucleus that contains all of our genetic information. We inherit 23 pairs of chromosomes from our parents. Each chromosome is made up of DNA molecules. DNA is composed of a string of four types of nucleotides:

  • adenine (A)
  • cytosine (C)
  • guanine (G)
  • thymine (T).

DNA is a double-stranded molecule in the shape of a “double helix”. Each nucleotide on a strand pairs with its partner nucleotide on the opposite strand. A always pairs with T, and C always pairs with G. DNA is the building block of human genetics, and makes each of us unique.

Individual segments of DNA make up our genes. Genes are often called the “blueprint for life,” since they tell each of our cells what to do. They also dictate our traits, such as eye color, height and skin pigmentation. Genes perform by telling a cell how to make proteins, which in turn tell our bodies how to function.

Understanding Inheritance

We inherit two copies of every gene from our parents — one copy from our mother and one copy from our father. These genes combine to make us unique. Our traits depend on the types of genes we inherit from our parents:

  • Dominant and Recessive Genes: Some genes are dominant, while others are recessive. If one parent passes on a dominant gene, and the other parent passes on a recessive gene, the dominant trait will overrule the recessive one. For example, if one parent has brown eyes (a dominant trait) and the other parent has green eyes (a recessive trait), their child will inherit the dominant trait and have brown eyes. The child would need to receive two genes for green eyes (or green eyes and another recessive eye-color trait) in order to inherit green eyes himself.
  • Co-Dominant Genes: Other genes are co-dominant, meaning neither is stronger than the other. An example of this is blood type. If one parent has Type A blood and the other parent has Type B blood, their child will have Type AB blood.
  • Polygenic Traits: Several traits are known as “polygenic.” This means that a variety of genes contribute to this particular trait. Skin color is one polygenic trait. Polygenic inheritance may also be responsible for some diseases, such as cancer or heart disease.

Genetic Mutations

DNA is constantly replicating itself. Usually it is a perfect system, but mistakes sometimes occur during replication, causing a genetic mutation. Some mutations happen spontaneously when DNA replicates itself during cell division. Others are brought about by outside forces, such as:

  • chemicals
  • environmental factors
  • UV radiation
  • viruses.

Some mutations are useful, leading to genetic diversity and keeping us healthy. Others have absolutely no effect at all. But some mutations can lead to diseases and genetic disorders, including:

  • cancer
  • color blindness
  • cystic fibrosis
  • sickle-cell anemia
  • Tay-Sachs disease.

Most inherited mutations are recessive. This means that a person will not have a disease like sickle-cell anemia unless he inherits two copies of the mutation that causes the disease. If a person receives only one copy, he becomes a carrier of that mutation. He runs a risk of passing the disorder on to his children, but he will not display the symptoms of the disease himself.

Genetic Testing

DNA testing is becoming an increasingly popular option among prospective parents. Genetic counselors can test for a wide variety of inherited diseases and advise parents on the health risks their offspring could face.

Adults can also use DNA testing to identify adult-onset genetic disorders and risks. Some of the genetic diseases DNA testing can trace include:

  • cancer
  • cystic fibrosis
  • Down syndrome
  • fragile-x syndrome
  • hemophilia
  • Huntington’s disease
  • Lou Gehrig’s disease
  • neurofibromatosis
  • muscular dystrophy
  • sickle-cell anemia
  • Tay-Sachs disease.

Genetic testing is painless and involves screening a cell sample — usually taken from the inside of the cheek, or in the case of a fetus, from the womb. Health care providers often offer genetic counseling to help parents make informed decisions about conceiving.

For adults, DNA test results can encourage steps to delay the onset of a disorder or even prevent the disease entirely. For example, if a person finds out that he has a high genetic risk of developing heart disease, he can increase his exercise level, watch what he eats and seek treatment from his doctor to help prevent the disease from occurring.

Resources

Pakhare, J.(2007). Genetic diseases: List of genetic disorders. Retrieved December 9, 2008, from the Buzzle.com Web site: http://www.buzzle.com/articles/genetic-diseases-list-disorders.html

Starr, B. (2004). Ask a geneticist. Retrieved December 9, 2008, from the Understanding Genetics Web site: http://www.thetech.org/genetics/ask.php?id=22

The Tech Museum of Innovation. (2004). Understanding genetics. Retrieved December 7, 2008, from the Tech Web site: http://www.thetech.org/genetics/art01_what.php