Mutation

What is a Mutation?A mutation is a change in the order of the A, G, T and C bases in a gene. This causes the changed gene to make a different protein which can alter the appearance or function of the cell and/or the organism.

The White Kermode Bear or Spirit BearThe White Kermode or Spirit bear is a black bear that had a mutation (change in DNA bases) in just one nitrogen base in one of its chromosomes when it was a fertilized egg. Just one base changes in 1 out of 10 bears. The mutated gene will not show it colour white unless a bear gets one mutated gene from each parent (it needs two mutated genes to show the white coat.).

The Inheritance of Spirit BearsThe gene for white colour in black bears is a recessive gene. As long as a bear has 1 normal black gene from 1 of its parents, the bear will be black. It takes 2 white genes for a bear to be white. The black gene shows its trait over the white gene.

The Spirit Bear Is Being Protected

The Spirit Bear is important in the traditional culture of the Tsimshian First Nation. The B.C. government has limited the amount of logging in the forests inhabited by the bears.

Albino Mutants (Organisms With a Mutated Gene)Many organisms have albino forms in which a single gene has mutated or changed (because the DNA bases have changed).

Different Kinds of Mutations

1. A base (A,G,T,C) may be deleted. …ACGTTACGA… may become …AGTTACGA…

2. A base (A,G,T,C) may be added. …ACGTTACGA… may become …ACGTGTACGA…

3. A base (A,G,T,C) may be substituted. …ACGTTACGA… may become …ACATTACGA…

Kinds of Mutations1. Positive Mutations are DNA changes that help an

organism to survive better.

2. Negative Mutations are DNA changes that harm an organism and make it less likely to survive. Most mutations (90% + of all mutations) are this type.

3. Neutral Mutations are DNA changes that have no harm or benefit for an organism.

Positive MutationsSome person who become infected with the HIV virus (normally causing the disease, AIDS), have developed mutations which prevent the HIV virus from infecting the helper T cells.

Modern wheat developed from a grass which mutated and doubled its number of chromosomes from 12 to 24.

Negative MutationsSickle Cell Anemia is one example of a negative mutation. Sickle cells are red blood cells which have a slightly different hemoglobin protein (HbS) from regular blood cells which have normal hemoglobin.(Hb). In conditions of low oxygen, sickle hemoglobin forms rods which stretch the red blood cells into sickle-like shapes.

Sickle Cells – A Negative Mutation

When sickle cells pass through capillaries, they get stuck and prevent blood flow which is life-threatening. Symptoms for persons with sickle cells include pain, lethargy (tiredness). Organs damaged by lack of oxygen include lungs, liver and kidneys.

A Single Nitrogen Base Mutation in DNA

Sickle hemoglobin forms when there is a single base mutation in DNA. This causes a new amino acid to replace the normal amino acid and this change makes the sickle hemoglobin function badly (becoming rods) in low oxygen conditions.

Inheritance of Sickle Cell Anemia (The Disease)Sickle cell anemia is caused by a mutated gene on a chromosome. Every person has two chromosomes of each kind – one from their mother and one from their father. If a person has one normal gene and one sickle gene, they are called a carrier and rarely feel the severe effects of sickle cell anemia. If a person has two sickle genes (one sickle gene from each carrier parent) then a person has only sickle cells and is very sick, likely to die at some point.

Sickle Cell InheritanceIf two parents are carriers of the sickle cell gene, the probability is that 50% of their children will be carriers, 25% normal and 25% having Sickle Cell Anemia.

Persons With African / Indian Ancestry More Likely to Have Sickle Cell Genes

In Africa, having the Sickle gene was partly beneficial because it protected persons from Malaria. Normal persons were not protected from Malaria and thus died more, leaving the Sickle gene to multiply in the African population.

Negative MutationsCystic Fibrosis is a disease caused by a mutation in a gene on a chromosome. There are more than 1300 different mutations (different changes in the DNA of this gene) that have been recorded. The normal gene codes for a protein that helps bring chloride ions into and out of the cell. When any of the 1300+ mutations occur, chloride ions build up, causing a thick mucous to form in passages which blocks passages in the lungs and pancreas.

Cystic Fibrosis Symptoms and TreatmentA person with Cystic Fibrosis has difficulty breathing and often gets lung infections. Pancreas secretions needed in digestion get blocked by the mucous. Therapy includes tapping and pommeling the chest and back to move the mucous out of air passage ways. Special air vibrating machines now accomplish this action.

Inheritance of Cystic FibrosisTo get the disease, Cystic Fibosis, a person must receive a mutated gene from both parents. If a person has one mutated gene and a normal gene, the person will be normal but will carry the gene and could pass it on to her/his offspring.

Neutral MutationsWhen a mutation has no positive benefits or negative affects, it is called a neutral mutation. The White Spirit bear mutation is considered neutral because it offers no advantage or disadvantage for the bear that is white. For a different organism, it could be an advantage (ex: an actic hare) or a disadvantage (a white mouse in the woods).

MutagensMutagens are substances or factors that can cause mutations in DNA. Viruses, cigarette smoke, pollutants, Hg, asbestos, certain chemicals and radiation all can cause mutations (changes in the base code) in the DNA.

What Viruses Do in Organisms

A virus attaches to a cell and inserts its DNA into the cell’s DNA. The virus’ DNA then controls the cell’s DNA and “tells” the cell to make hundreds of new viruses which causes the cell to burst, releasing the new viruses to re-infect other cells.

How Viruses Can Cause MutationsWhen certain viruses attach to cell DNA, they can cause misreading of nearby genes, damage nearby genes or cause mis-copying of normal genes. This can make changes or mutations in the host cell’s DNA.

Correcting Mutations With Gene TherapyGene therapy is an attempt to replace a faulty mutated gene with a healthy copy of the normal gene. At present it is a risky therapy and is only used for diseases without known cures.

Gene TherapyA virus (like a cold virus) is altered to make it harmless and a healthy gene is inserted into the virus. When the virus enters the body and its DNA attaches to a cell’s DNA, the healthy gene gets into the cell. The cell then must “switch on” the gene to get the good proteins needed.

End of Presentation