Human Genetic Disorders Biology

Mutations Sometimes genes are damaged or copied incorrectly. A change in a gene is called a mutation. Mutations are a source of the variation a species needs in order to adapt to changing conditions over time. Most mutations are harmful or neutral, only rarely are they beneficial.

Recessive Mutations Most mutations are passed from parent to offspring without being expressed. Although rare, most people are probably carriers for a number of genetic mutations. It is unlikely that two individuals with the same unexpressed mutation will mate and produce an offspring expressing the mutation.

Genetic Disorders Particular mutations have become more common in human populations. The harmful effects that some mutations produce are called genetic disorders. A person with a genetic disorder has inherited a defective gene from both parents.

Cystic Fibrosis Caused by a faulty transport protein. This mutation causes mucus accumulation in the lungs and pancreas, causing difficulty breathing and blocking proper food digestion. There is no cure, only treatment of symptoms.

Sickle Cell Anemia Results from faulty hemoglobin. This mutation causes the body to make an abnormal form of hemoglobin, making red blood cells looked deformed. Sickled cells are fragile and break down easily. Symptoms include fatigue, headaches, muscle cramps, and sometimes kidney or heart failure.

Hemophilia Results from a fault blood-clotting protein. This mutation causes the body to build a defective form of a protein needed to clot blood. Small cuts do not heal well and internal bleeding can be fatal. This trait is sex-linked, meaning it is transmitted on the X chromosome. Only boys will develop the disorder. There is treatment and children with hemophilia can lead normal lives.

Down Syndrome A genetic disorder caused by an extra chromosome 21. Features include extra folds in the upper eyelids, broad flattened noses, short stature, and varying degrees of mental retardation. Occurs in about 1 of every 1,000 births and is more common among babies born to older mothers. Mothers 45 and older have a 1 in 16 risk of having a child with Down Syndrome.

Genetic Counseling A genetic counselor can prepare a family pedigree or record that shows inheritance patterns over several generations. This can help determine the chance of being a carrier for that disorder. We also have genetic testing now and we can test for the presence of specific genes known to cause genetic disorders.

Finding Cures Most genetic disorders cannot be cured. Therapy is available for some. Techniques in genetic engineering can make it possible to cure genetic disorders by replacing copies of defective genes with copies of healthy ones. Gene therapy is an evolving science.