Image via Wikipedia

The word ‘mutation’ is derived from the Latin word ‘mutare’ which means change. Mutation is defined as permanent and spontaneous change of the genes or chromosomes which gives rise to changes in human traits.

Mutation is classified as somatic (when it occurs in somatic cells) and gametic (when it occurs in gametes). Somatic mutation, for example the brown spots in the iris of the eye cannot be passed on to the next generation while gametic mutation such as albinism can be passed on. An organism which has undergone mutation is called a mutant.

Types of Mutation

 

Image via Wikipedia

There are two types of mutation, namely gene mutation and chromosome mutation.

1.     Gene Mutation – Refers to a change in the chemical structure of a gene (when part of the DNA is changed) and causes certain change to the traits of an individual. Normally, only a single gene is involved and it may occur in a recessive or a dominant gene. Albinism, sickle-cell anemia and color blindness are caused by mutation in the recessive gene while Huntington’s disease is due to a mutated dominant gene.

 

Image via Wikipedia

2.     Chromosome Mutation – Occurs when there is a change in the structure (arrangement of genes) of the chromosome or a change in the number (an increase or decrease) of chromosomes. A change in the number of chromosome is due to the failure of the homologous chromosomes to separate during meiosis. A normal human has 46 chromosomes but chromosome mutation during the formation of gametes may result in an individual having 45 or 47 chromosomes.

Consequences of Gene Mutations

 

Image via Wikipedia

Albinism is caused by a mutated recessive gene which results in the absence of the melanin pigment in the skin, hair and iris of the eyes in humans and other animals. Organisms which suffer from albinism are called albinos.

Albinos have reddish eyes. Human albinos are very sensitive to sunlight and they have a high risk of getting cancer.

Another example of a hereditary disease caused by a mutated recessive gene is color blindness. The mutated gene for color blindness is associated with the X chromosome.

Image via Wikipedia

Males with the recessive color blind, females with the recessive color blind genes in both their X chromosomes (homozygous) are also color blind while females with only one color blind gene in one X chromosome have normal vision but are called carriers.

Both sexes, male and female can contract hereditary diseases such as color blindness and hemophilia. However, chances for males are higher because when the recessive gene is present, the disease can be shown easily because the Y chromosome does not carry an allele for the trait. Whereas for the female, she needs both the X chromosomes color blind.

Consequences of Chromosome Mutations

Image via Wikipedia

When individuals have an extra chromosome, it results in a condition called Down’s syndrome.

Males who have 47 chromosomes, which is 44 + XXY chromosomes instead of the normal 44+XY chromosomes suffer from a condition called Klinefelter’s syndrome. Such males are sterile with small testes, are mentally retarded and have female characteristics such as enlarged breasts and spare body hair.

Image via Wikipedia

Males who have an extra Y chromosome with genotype 44 + XYY have psychopathic tendencies.

Females with the genotype 44 + XO (less one X chromosome) suffer from Turner’s syndrome. Such females are sterile because of their non-functional reproductive organs and they often age prematurely.

Causes of Mutation

 

Image via Wikipedia

Mutations occur as a result of errors during meiosis or mitosis at a slow rate.

However, a number of factors called mutagens may increase the rate of mutation.

Examples of mutagens are nuclear radiation, chemical substances and harmful rays that can change the chemical structure of the genes resulting in mutation.

Nuclear radiation and harmful rays can penetrate into cells and destroy them.

Harmful rays such as ultraviolet rays and X-rays can kill living cells and cause cancer.

Chemicals such as mustard gas, benzene, herbicides, pesticides and dioxins can act on DNA of cells resulting in mutation.

Advantages and Disadvantages of Mutation

 

Image via Wikipedia

The advantages of mutation are: a) it gives rise to variation. b) It creates new species. c) It is the precursor to the evolution process.

Mutation gives rise to variation and new species which help organisms to survive and adapt in an ever-changing environment.

Examples are: a) According to research, 40 people in a town called Limone had very high cholesterol levels but this was not harmful to them. Investigation showed that they had a mutant gene which produced a new protein with unusual amino acid components. This protein is 10 times more efficient in removing excess cholesterol from the body. b) A new species of the paddy plant, MR 123 is more resistant to diseases, produces more grains with high protein content and matures faster.

Image via Wikipedia

Image via Wikipedia

The disadvantages of mutation are: a) it causes physical deformities. b) It causes genetic diseases.

Polydactylity is an example of a physical deformity found in humans but it is harmless. Individuals with such a condition have an extra finger on the hand or an extra toe on the lost.

Gene mutation gives rise to genetic diseases such as color blindness, albinism, hemophilia and retinoblastoma.

Chromosome mutation gives rise to hereditary diseases such as Down’s syndrome, Turner’s syndrome and Klinefelter’s syndrome.

The Hutch Gilford Progeria syndrome is causes by a mutated gene on chromosome number 1; it results in an accelerated ageing process seven to seven to ten times the normal rate. It affects 1 in every 100,000 – 1,000,000.