A gene mutation is defined as the permanent changes in the structure of the gene results in a mutation. Gene mutations vary from a small portion of the DNA molecule to a large part of chromosome. There are two types of mutations mainly:

1) Hereditary mutations:-
This kind of gene mutations are hereditary that is they pass from parents to the off spring. These mutations are present in the egg or sperm of an individual and pass to the next generation. These are not recoverable and remain in the person's body throughout their life.

2) Acquired Mutations:-
Acquired mutations are not hereditary but occur due to the environmental changes and alter the genetic makeup of an individual. Ultraviolet rays or X-rays are the examples which cause acquired mutations. There is a benefit of acquired mutations that they do not pass from parents to the off springs.

There are cases of gene mutations in which mutation occurs in the genes just after the egg and sperm fuse together to make an embryo. These are also called as new mutations. In this type of gene mutation, though a child contains mutation in his every cell but the history of his parents does not show any record of mutations. During the early embryonic stages, there are chances that mutations occur in some cells and some cells remain without a mutation, that's why when an organism develops, some of its cells will have the mutations and some will be without mutation that is healthy. Such types of mutations are also called as mosaicism.

Here are some diseases which are caused by gene mutations:-

1)Cystic Fibrosis:-
Cystic fibrosis is a single gene mutation. This disease is related with secretory glands of the body like sweat and mucus. This is a hereditary disease. Mostly lungs, liver and pancreas are affected by this disease.

When defect is caused in the gene CFTR, it results in the occurrence of the disease cystic fibrosis. CFTR is responsible for making a protein which causes the movement of components such as salt and water from in and out of the cells of the individual's body. If an individual is suffering from the disease of cystic fibrosis, he/she contains thick mucus and very salty sweat. It means that the protein responsible for these functions does not work properly. This protein causes other defects in the humans' body also. When the disease of cystic fibrosis gets severe, it means that there are other genes are also which are responsible in enhancing this disease. Symptoms include; abnormal salty taste of the skin and after the birth, the child can't take out stool properly.

2)Sickle Cell Anemia:-
Sickle cell anemia is also an inherited disease. If the disease appears in the body, it means, there are two genes one from the mother and the other from the father. The level of hemoglobin becomes abnormal in this disease. Hemoglobin is an iron containing protein and it is also responsible for giving the red color to the blood. It is the hemoglobin which is carries oxygen from the lungs in the blood and passes it to various parts of the body. During the disease of sickle cell anemia, red blood cells do not remain n their normal shape and become elongated. The HBB gene gives the red blood cells their spherical shape. When the defect occurs in this gene, cells do not remain in their normal shape. Sickle cell anemia is an autosomal recessive disease when one parent transfers the Hb S gene. But when both of the parents are carriers for this disease, then the off spring will definitely suffer from this genetic disease.

This disease is also genetic and occurs due to the mutations in gene sequence. Hemophilia is hereditary which disables the body cells to clot after the blood starts coming out of the body after some injury. Hemophilia usually occurs in males and there are rare cases of women suffering from hemophilia, because there is only one X chromosome in males while women have two X chromosomes. As it is known that the gene which causes mutation for hemophilia is present only on the X chromosome and not on the Y chromosome. As women have two X chromosomes so if she one X chromosome is carrier of hemophilia, then the other X chromosome will have the healthy allele which will code for healthy clotting. But when that defected allele or gene is present in the X chromosome of male, then there will be no possibility of male having the healthy allele on Y chromosome that is why this disease will become dominant in males.

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