chapter 15

A mutation is defined as

heritable change in the genetic material (any permanent change in the nucleotide sequence of DNA)

although RNA and protein molecules can be altered

they are not heritable and not technically considered mutations

Not al mutations cause a

chanage or significant effect on a protein

ultimate effect on RNA/protein may be a gain or loss of

functions, altered function, or no change in function

beneficial mutations

evolution form chimp to human

detrimental mutations

genetic disorders and extinction

Point mutation

a mutation that alters a single nucleotide (base) within the DNA

• can change the base sequence within the DNA

• base substitution: can be silent, missense, or nonsense

Can add or delete bases of the DNA sequence:

Addition (insertion) or deletion (loss) of a base: can result in a frameshift mutation

change the arrangement/ sequence of the codon

base substitution is when

one base is wrongly paired with another base during DNA replication

Some base pair substitiutions have little or no impact on protein function

• some alterations of nucleotides still indicate the same amino acids because of redundancy in the genetic code

• other changes lead to switches from one amino acid to another with similar properties

• still other mutations may occur in a region where the exact amino acid sequence is not essential for function

Some base pair substitutions may have a drastic effect

ex: sickle cell disease

Normal hemoglobin DNA : CTT

mRNA Normal hemoglobin : GAA

Mutant hemoglobin DNA: CAT

mRNA sickle cell hemoglobin : GUA

a base substitution mutation within a gene can result in three types of mutation to the codons of the mRNA

silent mutation, missense mutation , nonsense mutation

can change and effect the codon becoming a start or stop and effect mRNA and effect the protein

a frameshift mutation results from

the addition (insertion) and or deletion (loss) of nucleotides in a gene

cystic fibrosis

CFTR

sickle cell disease

HBB

marfan syndrome

FBN1

progeria

LMNA

tay sachs disease

HexA

several human genetic diseases are due to alterations to

large segments of DNA and chromosome structure

• these can be caused by external sources or problems in the cell cycle

four categories of structural changes

• deletion

• duplication

• inversion

• translocation (simple and reciprocal)

deletion chromosomal mutation

a segment of chromosomal material is removed

• most cause serious disorders or are lethal

Duplication chromosomal mutation

a section of chromosome occurs two or more times

• genes sequences can be repeated two or more times in a row and can occur in normal and abnormal chromosomes

inversion chromosomal mutation

an inversion is a chromosomal rearrangement that results in a change of direction of the DNA within a single chromosome

• occurs when a segment of a chromosome is broken in two places changes direction (reversed) and put back together

translocation chromosomal mutation

a segment of one chromosome is broken off and becomes attached to another chromosome

• can be simple (or nonreciprocal) or reciprocal

Spontaneous mutations

• occurs as a result of mistakes in natural biological processes

ex: DNA polymerase making an error during DNA replication that does not get corrected

Ex: normal metabolic reactions within the cell may produce toxic by products that can alter DNA sequence

there is no outside of cell influence or cause

induced mutations

occur as a result of exposure to environmental agents that can enter the cell and alter the structure of DNA

• mutagen, a chemical or physical agents that interacts with the DNA to cause mutations

examples of mutagen

• chemical agents (nicotine and benzo (a) pyrene)

• physical agents (x-rays and UV light)

• some viruses (papilloma viruses and hepatitis B virus)

spontaneous mutaiton examples

errors in dna replication

toxic metabolic products

changes in nucleotides structure

transposons

Induced mutation examples

chemical agents

physical agents

chemical mutagen agent

• nitrous acid

• 5-bromouracil

• 2-aminopurine

• nitrogen mustard

• ethyl methanesulfonate (EMS)

• Benzo[a] pyrene

Physical mutagen agent

x-rays

UV lights