Basis of Disease
is the passage of traits that are genetically determined. Inherited traits are
passed from parent to offspring. However, most traits are not strictly
determined by genes, but rather are influenced by both genes and environmental factors.
is a change in a DNA sequence that affects a gene. Mutations can result from
DNA copying mistakes made during cell division or environmental
exposure to things that affect DNA in the body, like radiation,
exposure to chemicals called mutagens or infection by viruses. There are two kinds of mutations.
- Germ-line mutations: Occur during cell division when reproductive cells (eggs
and sperm) are being made and can be passed on to offspring.
- Somatic mutations: Occur to cells that divide in the body throughout
one’s life (such as when healing from an injury or regularly replacing blood
cells) or from environmental exposure. These kinds of mutations are not passed on from parent to offspring.
Genotype vs. Phenotype
The exact DNA sequence of an individual is referred to as that person's
genotype. The collection of all observable and measurable traits of that
individual is the person's phenotype. It is not which genes you have (genotype), but how
those genes are expressed and interact with each other during development (phenotype) that
makes you different from another individual of the same species.
Basis of Disease
disease or health condition has a genetic component. Through molecular biology research we are
just beginning to understand the function of suspected disease-related genes
and how they work in normal and "at-risk" individuals.
- Single-gene disorders:
Single-gene disorders are caused by DNA changes in one particular gene, and
often have predictable inheritance patterns. More than 10,000 human disorders are caused by a mutation in a single gene. Each individual single-gene disorder is very rare, but as a whole, these kinds of disorders affect about one percent of the population. Single-gene disorders can be caused by inheritance of either dominant or recessive genes. The difference is shown below in illustrations developed by Mayo Clinic.
Dominant single-gene disorders include Huntington's disease and inherited forms of high cholesterol.
Recessive single-gene disorders include cystic fibrosis and sickle cell anemia.
Source: Republished with permission from Mayo Clinic, Genetic Testing, 2016 (http://www.mayoclinic.org/tests-procedures/genetic-testing/multimedia/genetic-disorders/sls-20076216?s=3).
For more information on single-gene disorders, visit:
- Complex diseases:
For the most part, complex
diseases are caused by a combination of genetic, environmental and lifestyle
factors, most of which have not yet been identified. The vast majority of
diseases fall into this category, including several congenital defects and a
number of adult-onset diseases. Some examples include Alzheimer's disease,
asthma, multiple sclerosis, osteoporosis, connective tissue diseases and autoimmune diseases.
Cancer is a group of diseases characterized by uncontrolled cell growth.
Cancer is caused by a mutation, or accumulation of several mutations, resulting
in a breakdown of the normal regulatory controls that keep cell division in
check. These mutations can be inherited, can be caused by errors in DNA replication
or can result from exposure to mutagenic viruses or chemicals. A cancerous tumor can spread to other parts of
the body and, if left untreated, be fatal.