What is a mutation?
Mutations are a change in the structure or amount of an organisms DNA. Mutations arise spontaneously and at random
Frequency of mutations
Mutations are rare. In humans it is estimated that there is 1 mutation per 15-30 million base pairs. Mutation rates differ in different genes and different organisms
Types of mutations
- Single gene mutations
- Chromosome structure mutations
- Polyploidy
Single gene mutations
These mutations involve a change in one of the base pairs in the DNA sequence of a single gene. Also known as point mutations. These may occur in the protein-coding sequence or the regulatory sequences which control expression of the gene.
There are 3 types of point mutations (gene mutation):
- Deletion
- Insertion
- Substitution
Problems caused by substitution: Sickle cell anaemia
Genetically transmitted disease
Caused by abnormal hemoglobin (protein)
Known as a point mutation (substitution)
Problems caused by insertion and deletion
- Brings about a major change in the protein which is made since a large section of DNA is affected
- Many amino acids are altered which results in a non-functional protein (known as a lethal gene)
- This is known as a frame shift mutation
- Sometimes a metabolic pathway enzyme is affected and the pathways is disrupted e.g. Phenylketonuria
Phenylketonuria
- Gene mutation results enzyme not produced that changes phenylalanine to tyrosine
- Phenylalanine concentration builds up within body of the newborn baby
- Phenylalanine is converted into toxic substances
- The toxic substances cause irreversible damage to the developing brain
RNA splicing is important in __________. Mutations in the area that marks the start or end of an intros, may lead to one or more _______ not being removed. This will lead to a creation of a protein that _______ function properly
Creating the mature mRNA transcript before it is translated into a protein
Introns
Doesn’t
Thalassemia
Thalassemia is a type of anaemia (similar to Sickle Cell) where a police site mutation has caused a defect in the synthesis of hemoglobin. Thalassemia, a disease caused by a defect in hemoglobin synthesis, is caused by a splice site mutation
Types of chromosome structure mutation
- Duplication
- Inversion
- Translocation
- Deletion
Duplication
- duplicated genes may undergo mutation
- this can introduce a new characteristic that may or may not be advantageous
- duplication of a gene produces a second copy of the gene which is free from selection pressure (it can become altered without affecting the original genes function)
Inversion
- reversal of sequence
- problems with pairing and crossing over in meiosis
- often non-viable gametes
Deletion
- drastic effect
- humans: cri du chat (mental retardation)
Translocation
- sections attaching to non-homologous partners
- problems win pairing in meiosis
- translocation involves transfer of genes from one chromosome to another
- this results in problems pairing chromosomes during gamete formation and leads to non-viable gametes
Polyploidy
Polyploidy is duplication of all the chromosomes resulting in extra sets of chromosomes. It is the result of an error during gamete formation: error of chromosome separation during gamete formation (due to total spindle fiber during meiosis)
Polyploidy in plants
Polyploid plants are normally larger, and have increased seed and fruit size. This is of economic importance. Hybrid plants (mixing genes from two different breeds) have a selective advantage over non-polyploid plants. Polyploid plants (hybrid) with an uneven number of sets of chromosomes are sterile. This allows the production of sterile seedless fruits e.g. Bananas
