Ch 12-4 Genetic Mutations

What is a Mutation? Changes in the genetic code of DNA Original DNA: ATAGGCCTAGCAGTCG Mutated DNA: ATAGGGCTAGCAGTCG OR Mutated DNA: ATAGGCCTAGCAAGTCG Mutated DNA: ATAGGCCTAGAGTCG

Mutations can occur in two different types of cells: Somatic (body) cells Ex. Skin, heart, liver, lung, blood, muscle Gamete (sex/reproductive) cells Ex. Sperm, Egg

Mutations in somatic cells Usually result in killing that body cell only. Usually do not affect the individual. Exception: If the mutation occurs in the DNA that controls the cell cycle (division), it can result in cancer. Can NOT be passed on to the next generation

Mutations in Gamete(sex) cells Means that every cell of the developing fetus/baby will have that mutation. Usually do not affect the individual with individual with the genetic disorder. Can be passed on to the next generation

There are two types of mutations that can occur. Gene mutations Mutations that produce changes in a single gene Chromosomal mutations Mutations that produce changes in parts of or whole chromosomes.

Type of Single Gene Mutations -POINT

Two Types of Single Gene Mutations Point Frameshift

1. Point Mutation-a single point in the DNA sequence is affected. Can be a substitution in which one base is changed into another.

1. Point Mutation-a single point in the DNA sequence is affected. Can be a substitution in which one base is changed into another base during replication.

Example: Original Sequence DNA:                TAC    GCA    TGG    AAT mRNA:             AUG   CGU    ACC   UUA Amino Acid:    Met  -   Arg  -  Thr   -  Leu (In this DNA sequence notice the 5th base in the DNA sequence has been changed) Mutated Sequence DNA:             TAC    GTA    TGG    AAT mRNA:           AUG   CAU    ACC    UUA Amino Acid:  Met  -   His  -   Thr   -   Leu

Point mutations usually affect no more than a single amino acid. The protein may be slightly affected or not affected at all. Ex using a sentence. THE FAT CAT ATE THE RAT THE FAT CAT ATE THE HAT

Types of Gene Mutations – Frame Shift

2. Frame Shift Mutation A single gene or nitrogen base is deleted or inserted from the mRNA sequence causing a shift in the “reading frame” of the genetic code. If a nucleotide is inserted or deleted, the bases are still read in groups of three, so every codon after is changed.

Example: DNA:         TAC    GCA    TGG    AAT mRNA:      AUG   CGU    ACC    UUA Amino Acid: Met  -  Arg  -  Thr   -  Leu *(Notice in this DNA sequence a T has been added to the sequence after the second base) DNA:        TAT   CGC   ATG    GAA   T mRNA:     AUA  GCG    UAC   CUU   A Amino Acid: Iso  - Ala  -   Tyr  -  Leu

The affect of frame shift mutations is usually more dramatic than point mutations. Frameshift mutations may change every amino acid that follows the point of the mutation. Frameshift mutations can alter a protein so much that it is unable to perform its normal functions.

Example using a sentence THE FAT CAT ATE THE RAT  TEF ATC ATA TET HER AT

Chromosomal Mutations: Involves changes in the number or structure of chromosomes Can change the locations of genes on chromosomes, and the number of copies of some genes

Chromosomal Mutations

5 types of Chromosomal Mutations: 1.Deletion-Loss of all or part of a chromosome. 2.Duplication- extra copies of parts of the chromosome are made. 3.Inversion- reverses the directions of parts of a chromosome. 4.Translocation- Part of a chromosome breaks off and attaches to another chromosome. 5.Non-disjunction- when chromosomes fail to separate during meiosis.

Non-disjunction Results in abnormal numbers of chromosomes. Typically you have 2 of each. Trisomy (3) means a person has an extra copy of a chromosome. Monosomy (1) means a person is missing a copy of a chromosome.

What causes mutations? Usually during DNA replication. Sometimes from Environmental Factors UV radiation Chemicals (lead, asbestos) Pollution Tobacco smoke Viruses