Human Genetic Mutations

Mutations Mutations are a result of a change in the DNA sequence A different protein or a dysfunctional protein may be produced If mutations occur in sex cells they may be passed on to the next generation. A mutation occurring in somatic cells may be a problem for the individual but will not be passed on to the offspring.

Chromosomal Alterations Mutations Mutations may be classified as Chromosomal Alterations or Gene Mutations Chromosomal alterations are generally more severe because many genes are usually involved.

Chromosomal Mutations Any change in the structure or number of chromosomes Large scale -Affects many genes

Gene Mutations Small scale: one gene is affected Any change to the DNA sequence of a gene Nucleotides/Bases may be added, missing, or changed

Significance of Mutations Most are neutral Eye color Birth marks Some are harmful Cystic Fibrosis Down Syndrome Some are beneficial Sickle Cell Anemia to Malaria Immunity to HIV

What Causes Mutations? There are two ways in which DNA can become mutated: Mutations can be inherited. Parent to child Mutations can be acquired. Environmental damage Mistakes when DNA is copied

5 Types of DNA alteration Deletion Duplication Inversion Translocation Non-Disjunction

One or more genes are removed Chromosomal Deletion One or more genes are removed Example: Wolf-Hirschhorn syndrome (severe mental retardation) Cri du chat syndrome (mewing sounds, mental retardation)

Chromosomal Duplication A segment of genes is copied twice and added to the chromosome Example: Charcot–Marie–Tooth disease (high arched foot, claw feet, confined to a wheelchair)

Chromosomal Inversion a segment of genes flip end-to-end on the chromosome Example: Four-Ring Syndrome (cleft pallate, club feet, testes don’t descend)

Chromosomal Translocation Material is swapped with another chromosome Example: Burkitt’s Lymphoma (cancer of the lymph nodes, in children)

Nondisjunction Chromosomes FAIL TO SEPARATE during meiosis Meiosis I Nondisjunction Meiosis II Nondisjunction

Nondisjunction Produces gametes (and therefore a baby) with one missing chromosome or one extra chromosome

Too much or too little DNA is bad! KEY POINT #1 Too much or too little DNA is bad!

Gene Mutations: 2 Types Point Mutation Frameshift Mutation

Point mutation Only one nucleotide changes, but it makes a different protein

Point Mutation One base (A, T, C, or G) is substituted for another 3 Possible Consequences: nonsense mutations: code for a stop, which can translate the protein missense mutations: code for a different amino acid silent mutations: code for the same amino acid

Gene Mutations Point Mutations – changes in one or a few nucleotides Substitution THE FAT CAT ATE THE RAT THE FAT HAT ATE THE RAT Insertion THE FAT CAT XLW ATE THE RAT Deletion THE FAT ATE THE RAT

Frameshift Mutation One or more bases (A, T, C, or G) are added or deleted Caused by: Insertion: adding a base Deletion: removing a base

Frameshift Causes every codon in the DNA sequence to be changed after the mutation: Insertion- one or more bases are added Deletion- one or more bases are removed A

Causes of Mutations spontaneous occur during DNA replication Caused by MUTAGENS physical, ex: radiation from UV rays, X-rays or extreme heat or chemical (molecules that misplace base pairs or disrupt the helical shape of DNA).

Gene Mutations KEY IDEA: A mutated gene will make a mutated protein Mutant proteins are trouble! They do not go where they are supposed to go They do not do what they are supposed to do

KEY POINT #2 Mutation of a gene = Mutant protein Dysfunctional proteins cause the symptoms of the disorder

Length of Telomeres telomeres Telomeres are structures at the ends of chromosomes that shorten with each cell division. After 50 divisions, the shortened length of telomeres causes mitosis to stop.