Mutations
What is a mutation?
• ANY change in the genetic material (DNA)
• Mutations may be spontaneous or caused by mutagens (physical and chemical agents)
• Mutations are the primary source of genetic variation (not all are harmful)
• Mutations may provide an organism with a selective advantage (evolution)
Types of Mutations
A. Chromosomal Mutations
- large-scale mutations
- affect many genes on a chromosome
B. Gene Mutations
- small-scale mutations
- affect only one gene and therefore one protein
Types of Mutations
Chromosomal Mutations
• Inversion
• Duplication
• Deletion
• Translocation
• Nondisjunction
Gene Mutations • Point Mutations
• Silent
• Missense
• Nonsense
• Frameshift Mutations
• Insertion
• Deletion
Chromosomal Mutations
Chromosomal Mutations
• Mutations result from errors in mitosis or meiosis
• Changes in chromosome number often result in new phenotypes, including sterility caused by triploidy and increased vigor of other polyploids
• Changes in chromosomes number often result in human disorders with developmental limitations
Polyploid Plants
• Multiple copies of each chromosome instead of only 2 copies of each chromosome (2n)
Human Disorders
• Trisomy 21 (Down Syndrome) – three copies of chromosome 21 instead of two
• Turner Syndrome (XO) – female with one X chromosome instead of two
• Both disorders result from nondisjunction of chromosomes during Meiosis
Chromosomal Mutation: Nondisjunction
Other Chromosomal Mutations
Gene Mutations
Gene Mutations
Nucleotide-Pair Substitutions
• Replacement of one nucleotide and its partner with another pair of nucleotides
• Results in a silent, missense or nonsense mutation
Silent Mutation
• Mutation has no effect on the encoded protein due to the redundancy of the genetic code
Missense Mutation
• Changes one amino acid to another
• May have little effect on the protein or drastically change the proteins function
Sickle Cell Anemia • Example of a missense mutation
• Mutation affects a crucial area of the hemoglobin protein
Nonsense Mutation
• Changes an amino acid into a stop codon
• Translation terminated prematurely
Nucleotide-Pair Insertions and Deletions
• Additions or losses of nucleotide pairs in a gene
• Result in frameshift mutations
Frameshift Mutations
• Usually affect the resulting protein more dramatically than other gene mutations
Effects of Mutations • DNA mutations can be positive, negative or
neutral based on the effect or lack of effect they have on the resulting nucleic acid or protein
• Example: Heterozygote Advantage
– Tropical Africa where Malaria is common
Heterozygote Advantage
Effects of Mutations
• Changes in genotype may affect phenotypes that are subject to natural selection
• Genetic changes that enhance survival and reproduction can be selected by environmental conditions
• Example: Antibiotic resistance and pesticide resistance mutations
Antibiotic Resistance
Pesticide Resistance