Mutations What is a mutation? ANY change in the genetic material - - PowerPoint PPT Presentation

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
• f only 2 copies of each chromosome (2n)

Human Disorders

• Trisomy 21 (Down Syndrome) – three copies
• f 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