Mutations

Mutations mutation – a change in DNA sequence of bases mutagen – agents that cause mutation, such as: 1) radiation 2) chemicals 3) viruses 4) natural causes (errors in replication)

Types of Mutations I. Gene mutations – involve a single nucleotide or many nucleotides within one gene 1. frameshift mutations – loss or addition of nucleotides that disrupts codon 2. point mutations – change in only one nucleotide (substitution)

Types of Mutations II. Chromosomal mutations – involve entire chromosomes or large pieces of chromosomes A. Chromosome mutations involving pieces of chromosomes: 1. deletion – a piece of a chromosome breaks off and is lost *most are lethal, killing the organism 2. duplication – part of a chromosome breaks off and is incorporated into its homologous chromosome

Types of Mutations 3. translocation – a chromosome part breaks off and attaches to a different, non- homologous chromosome 4. inversion – part of a chromosome breaks off, turns around, & reattaches in the reverse order

Types of Mutations Chromosome mutations involving whole chromosomes: 1. monosomy – missing one chromosome in a pair ex: XO (Turner Syndrome) 2. trisomy – having one extra chromosome in a pair ex: XXY (Klinefelter Syndrome) or XYY (Jacob Syndrome) *all monosomies, trisomies are a result of nondisjunction

nondisjunction – failure of chromatid pairs to separate in anaphase other monosomies/trisomies include: Patau Syndrome (Trisomy 13) Down Syndrome (Trisomy 21) Edward Syndrome (Trisomy 18) *Cri-du-chat – missing short arm of chromosome #5 (deletion)

Karyotype karyotype – procedure done to detect chromosome abnormalities Steps: 1) tissue sample is taken 2) cells are grown in a flask for a few days 3) chemical is added to halt cell division in metaphase 4) chromosomes are photographed and enlarged 5) chromosomes are cut out & paired up by size, shape, & centromere location from largest to smallest