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