A gene is a molecular segment of DNA on a chromosome that has a hereditary effect. It regulates the traits of living organisms and indirectly affects their life activities. When a gene is mutated, which is commonly referred to as a mutation, the traits of the organism also change. In humans, this may lead to the development of rare diseases that are usually congenital and difficult to cure. Some mutations in plants may cause the species to acquire new traits, potentially improving the traits of the organism, but most mutations are harmful to the living organism.

Human chromosomes have twenty-three pairs of chromosomes, of which chromosome 21 normally has two, and patients with Trisomy 21 have an extra chromosome 23. Patients show congenital stupidity, patients usually have a special face, short stature, low intelligence level, and severe developmental delay. This disease was the first chromosomal genetic disorder discovered in humans. At present, with the development of science and technology and medical level, pregnant women can be screened during pregnancy to prevent.

Sickle cell anemia is also a human disease caused by gene mutation. Normal hemoglobin peptide chain in the sixth position is glutamic acid, and the patient's sixth position after the mutation into valine, the two amino acid hydrophobicity is different, so that after the mutation of the red blood cells from the flat round shape into a sickle type. Sickle-shaped red blood cells are prone to hemolysis and blockage of capillaries, resulting in anemia and damage to tissues and organs. Clinically, blood transfusion and medication are usually used to intervene.

Three, genetic variation and cancer

There are proto-oncogenes and oncogenes in the human body, which control the proliferation and apoptosis of cells in the human body. The ****same role of the two make the cells in the body to maintain a homeostatic balance, once these genes changed, suddenly gained the function of enhancement or loss of function, these mutation effects superimposed on each other, which may ultimately lead to an imbalance in the homeostasis, some uncontrolled cells undergo oncogenic mutation, a large number of proliferation of tumor cells, which triggers cancer.