Genetics is the process in which parents pass certain genes onto their children. An abnormal gene that is passed down through the family may have only minor consequences, or it may have a dramatic impact on one's quality of life. Abnormal genes result due to single-gene defects or chromosomal disorders, according to Medline Plus. Cystic fibrosis, sickle cell anemia, Down syndrome and color vision deficiency are common genetic diseases that involve either single-gene defects or chromosomal disorders.
Cystic Fibrosis
Cystic fibrosis is a common inherited genetic disease within the Caucasian population of the United States, according to the Genetics Home Reference, a website maintained by the National Institutes of Health. The disease occurs in one out of 2,500 to 3,500 Caucasian newborns. Cystic fibrosis affects the mucus glands and causes progressive damage to the respiratory and digestive systems.
Individuals with cystic fibrosis tend to produce abnormally thick and sticky mucus. The thick mucus can obstruct the airway, causing severe breathing problems along with bacterial infections in the lungs. Permanent lung damage, including scar tissue formation (fibrosis) and cysts within the lungs, result over time due to excessive mucus buildup and bacterial infections.
Sickle Cell Anemia
Sickle cell anemia is an inherited genetic disease which affects the structure of family members' red blood cells. Medline Plus describes the red blood cells (RBCs) as being crescent-shaped ("sickles"), as opposed to the normal disc shape.
Hemoglobin S is an abnormal type of hemoglobin (protein within RBCs) that distorts the shape of the red blood cells. The distorted, crescent-shaped cells are fragile and deliver less oxygen to the body's tissues. The fragile RBCs are more prone to break into pieces and disrupt blood flow.
In order to have sickle cell anemia, it must be inherited from both parents. An individual who inherits the hemoglobin S gene from one parent and normal hemoglobin A from the other will have the sickle cell trait. Sickle cell anemia is commonly seen in individuals from South and Central America, the Caribbean and the Middle East.
Down Syndrome
Down syndrome is a chromosomal condition which occurs in approximately one out of 740 newborns, according to the Genetics Home Reference website. Down syndrome occurs from each cell in the body containing three copies of chromosome 21 instead of two copies; this is termed "trisomy 21." The extra chromosome causes disruption in normal development, causing the characteristic features of this syndrome: mild to moderate cognitive disability, a distinctive facial appearance and poor muscle tone during infancy.
Color Vision Deficiency
Medline Plus states that color vision deficiency is due mostly to genetic factors. The most common color vision defect is red-green, where individuals have difficulty in color perception, especially in distinguishing between shades of red and green. In people of northern European decent, the red-green color vision defect occurs in approximately 8 percent of males and 0.5 percent of females. Individuals inherit the red-green color vision defect gene on a mutated X chromosome.
