Changes in the nucleotide sequence of DNA or mRNA Mutations Changes in the nucleotide sequence of DNA or mRNA

Mutations Changes in the nucleotide sequence of DNA or RNA that code for a protein Mutations are caused by mutagens (means “to generate a mutation”) Examples: UV Radiation Cigarette Smoke Viruses Chemicals: Laboratory, pesticides, insecticides

Point Mutations One nucleotide base is replaced with another (A single nucleotide mutates thus affecting one codon.) It’s like changing one “word” in a DNA sentence.

Silent Point Mutation For Example This is a harmless mutation. Since many amino acids have multiple codons, it is possible that a mutated codon will still translate into a correct amino acid. For Example Original Sequence: G A A  G A G mRNA: C U U  C U C Amino Acids: Leu  Leu

Missense Point Mutation This mutation changes the amino acid coded for (MIStake). This is seen in the mutation that causes Sickle Cell Anemia For Example Original Sequence: C T T  C A T mRNA: G A A  G U A Amino Acids: Glu  Val Glutamate Or glutamic acid becomes Valine

Sickle Cell Anemia

Frameshift Mutations These mutations alter the codon sequence and shift the ‘reading frame’ (A reading frame is a set of 3 consecutive nucleotides (codon) read in the 5’  3’ direction). It’s like changing the DNA “sentence.” Frameshift mutations are normally very serious. If the codons aren’t read correctly, they will be translated into incorrect amino acids and make nonfunctional proteins.

Insertion: adding nucleotides to the sequence Original sequence: THE BIG TAN DOG RAN Original with Insertion: THE BOI GTA NDO GRA N For Example Original Sequence: CAT TGA  CAT ATG A mRNA codons: GUA ACU  GUA UAC U Amino Acids: Val Thr  Val Tyr --

Deletion: taking nucleotides out of the sequence Original sequence: THE BIG TAN DOG RAN Original with Deletion: THE BGT AND OGR AN For Example: Original Sequence: CAT TGA  CTT GA mRNA codons: GUA ACU  GAA CU Amino Acids: Val Thr  Glu --

Chromosomal Mutations Mutations in chromosome structure Deletion: sections of the chromosome are missing Duplication: sections of a chromosome are repeated

Mutations in Chromosome Number Monosomy: only one copy of a chromosome Turner Syndrome: when a female has only one X chromosome. Females with this condition have short stature, are sterile and have other physical abnormalities.

Trisomy: one extra copy of a particular chromosome (three copies total) Down Syndrome (trisomy 21): mental retardation, short stature, wide set eyes Occurs in about 1 in 691. Most individuals live to adulthood, but may have shorter lifespan than average

Who is Affected? Somatic Cells Gametes If a mutation happens in a body cell, only the person that the mutation occurred to will be affected Mutations in body cells can lead to cancer Gametes If a mutation happens in a sex cell, only the organism created from that sex cell will be affected. Mutations in sex cells affect future generations and this is a cause of evolution, i.e. change in DNA over time