Mutations

• These are errors made in the DNA sequence that are inherited.

• These may have negative side effects, no side effects or positive side effects.

Negative side-effects

• Some mutations may lead to a the development of a disease.

• Cystic fibrosis – mutation in the cystic fibrosis transmembrane regulator

Positive Mutations

• The human brain occurred through mutation.

• Caused a natural selection and the larger brains prevailed.

No effect

• The side effect may not surface immediately – especially eukaryotes

• We are diploid organisms meaning that we cancel the mutations out.

• If humans were haploid in nature much of the world population would be gone as we carry so many mutations.

Types of Mutations

• Silent mutations– No effect on the operation of the cell– Usually occurs in the introns of DNA– This means that post-transcription

modification removes this mutation

• Mutation can also be silenced through the redundant nature of the genetic code.

• Eg. Phenylalanine – UUU, UUC on mRNA

• Mistakes made during transcription or if a mutation is made and the third base is replaced with a G instead of an A – phenylalanine will still be created.

Missense mutation

• A mutation that results in the single substitution of one amino acid in the resulting polypeptide

• Change in the base sequence of DNA alters a codon – leading to a different amino acid in the sequence.

• Sickle cell anemia

• Normal red blood cell• Round flexible able to

pass through tiny blood vessels.

• Sickle cell• Looses flexibility• Is rigid and blocks

blood vessesls depriving the area of blood supply

Nonsense mutations

• Mutation that converts a codon for an amino acid into a termination codon.

• During translation only part of the protein will be created and the fragment may be digested by proteases.

• Often lethal to the cell

Substitution and Deletion

• Missense and nonsense mutations occur because of substitutions or deletions of a base pair.

• Substitution – replacement of one base in a DNA sequence by another base

• Deletion – the elimination of a base pair or group of base pairs for a DNA sequence.

• Point mutations – if only one base pair.

• By removing a base pair, it results in different base pairs being read.

• This will cause a drastic change in protein structure.

Insertion

• The placement of an extra nucleotide in a DNA sequence.

• Because DNA is read in triplets of nucleotides, and will cause different amino acids.

Frameshift Mutations

• Causes the reading frame of codons to change

• This results in different amino acids being incorporated into the polypeptide.

• Insertion and deletion can be considered Frameshift mutations, if they result in less than three codons being shifted.

• 3 nucleotides can be less serious.

Translocation

• The transfer of a fragment of DNA from one site in the genome to another location.

• A segment of a chromosome breaks and releases a fragment – this happens as the same thing is happening to another chromosome.

• The two fragments switch places – disrupting normal gene structure.

• This new segment can be transcribed and translated.

• New protein with an altered function.

• Some leukemia are a result of this.

Transposable Elements

• Segments of DNA that are replicated as a unit from one location to another on chromosomal DNA

• They move from one location to another, making genes inactive.

• Various colours of Indian corn are a result of Transposable genes - McClintock

Could this happen???

•

Inversion

• Reversed its orientation in the chromosome

• No gain or loss of genetic material.

• Some genes may be disrupted.