Mutations

Curly winged fruit flies Drosophila, short leg bassett hounds and seedless grapes are all examples of mutations

Mutations- definition

Mutation is a change or a mistake in DNA replication. Mutations can arise in from changes in individual genes or changes in the arrangement of genes on a chromosome

Types of mutations

There are two types of genetic mutations

1. Gene mutation 1. point mutation2. chain termination mutation 3. frameshift mutation

2. chromosomal mutation

Point Mutation

A point mutation is a single base pair change by physical or chemical means, where a nucleotide is replaced by a different type.

A nucleotide can have a BASIC SUBSTITUTION of a base pair.

Ex. Guanine changed to Adenine

Basic substitutions

There can be three outcomes for a basic substitution

1) silent mutation- NO EFFECT– ex. UCU, UCC, UCA, UCG are all the mRNA cod

e for Serine amino acid. These changes would have no effect.

– Also there are many genes which do not have an effect on the body, a change in these genes would not cause a change

Basic substitutions Cont.

2) Neutral effect- A mutation that would change the structure of the protein but have little effect on its function

3) Drastic effect- a small change in one AA would seriously effect the structure and function of the protein– ex. Sickle cell Anemia- a change in one AA

changes the shape of the hemoglobin of the RBC

Deletion

A deletion is when nucleotide is left out of a sequence of AA. Leaving out a nucleotide will cause a shift in the DNA and result in a synthesis of a polypeptide with an altered AA sequence.

Point mutations

Insertion

Similar to deletion, a nucleotide inserted in a sequence can cause a mutation in the protein beyond the point of the extra nucleotide.

In both deletion and insertion the polypeptide formed by the mutated gene, if one can be formed at all, is usually not functional.

Chain Termination Codon mutation

There are three codons ( Three base pairs) that tell the AA to stop adding to the proteins - UAA, UAG, UGA. When tRNA sees this code it stops making the protein. If there is a change in one of these codons it will have a lethal effect since the protein will stop growing or continue to grow.

Chromosomal mutations

Changes can occur in the chromosome as well as in the genes. Chromosomal mutations can happen in different ways.

Ex. a piece of the chromosome may break off or lost during mitosis.

Some of the chromosomal mutations can be repaired, others repair themselves in correctly.

Chromosomal mutations

Cancer

We now know that normal cells can be transformed into malignant cancerous cells. Gene mutations are ultimately to blame. Mutant forms of genes, ONCOGENES, result in abnormal proteins that disrupt the normal reproduction of cells and cause cancer. Oncogenes can be caused by a number of ways- by carcinogens (cancer causing substance (smoking, chemicals ); UV or X-rays

Cancer pictures

Mental retardation

A gene mutation responsible for a form of mental retardation affecting one in 600 males has been located on the X chromosome.

Mutation Disease- Sickle cell anemia

One in 500 people of African decent has sickle cell anemia, which is a disease that changes the shape of the hemoglobin protein. There is just one nucleotide difference in the sequencing of this protein. These blood cells can block capillaries in the body and cause pain, fever or even strokes and paralysis. Most people don't live past 40 years of age.

Benefits of mutations

Although most people think of mutations as harmful to or individual they can be helpful to an organism. Mutations of genes is cause of natural variation and one of the ways that organisms evolve. Gene mutations can have helpful results, allowing us to adapt to changes in the environment and survive as a species.

Examples of genetic diseases-Inherited or mutation

Acute intermittent porphyria

adult polycyctic kidney disease

albinism alkaptonuria BRCA breast cancer cystic fibrosis down syndrome Duchenne muscular dystr

ophy

fragile x syndrome hemophilia Huntington disease Neurofibromatosis Phenylketonuria Polyposis of the colon Sickle cell Anemia Tay-Sacs disease Thalassemia