MUTATIONS
Biology I
Brandon High School
What is a Mutation?
 A mutation is a permanent change in the DNA
sequence of a gene. Mutations in a gene's DNA
sequence can alter the amino acid sequence of
the protein encoded by the gene.
There are two main types of mutations:
1. Chromosomal Mutations
2. Gene Mutations
TYPES OF MUTATIONS
• Gene Mutation
• Point Mutation
• Frameshift Mutation
• Chromosomal Mutation
•
•
•
•
•
Deletion
Duplication
Inversion
Translocation
Nondisjunction
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
CHROMOSOMAL
MUTATIONS
• Any change in the
structure or number
of chromosomes
• Large scale: Affect
many genes
WHAT ARE CHROMOSOMES?
• Humans have 23 pairs of
chromosomes, with one
chromosome from each
parent.
• The chromosomes are
coiled up DNA.
• Under normal conditions
all of the chromosomes
are inherited in tact.
 POINT MUTATIONS~ THESE AFFECT ONE
NUCLEOTIDE, BECAUSE THEY OCCUR AT A
SINGLE POINT IN THE DNA SEQUENCE &
SUBSTITUTES ONE NUCLEOTIDE FOR
ANOTHER.
DNA:
mRNA:
AA:
DNA:
mRNA:
AA:
Example
TAC GCA TGG AAT
AUG CGU ACC UUA
Met Arg Thr Leu
 Substitution
TAC GTA TGG AAT
AUG CAU ACC UUA
Met Hist Thr Leu
POINT MUTATION
• One base (A, T, C, or G) is substituted for another
• Can Cause: Sickle-cell anemia
• 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
 FRAME SHIFT MUTATIONS~ THESE INCLUDE
INSERTING A EXTRA NUCLEOTIDE OR DELETING
A NUCLEOTIDE, WHICH SHIFTS THE “READING
FRAME” OF THE GENETIC MESSAGE
DNA:
mRNA:
AA:
DNA:
mRNA:
AA:
TAC GCA TGG AAT
AUG CGU ACC UUA
Met Arg Thr Leu
 Insertion
TAT CGC ATG GAA T
AUA GCG UAC CUU A
Ile
Ala Tyr Leu
 Environmental factors including radiation,
chemicals, and viruses, can cause
chromosomes to break; if the broken ends do
not rejoin in the same pattern, this causes a
change in chromosomal structure.
DELETION
•  Deletion – one or more genes are removed.
• This is a type of mutation in which an end of a
chromosome breaks off or when two
simultaneous breaks lead to the loss of a
segment.
DUPLICATION
•  Duplication is the copying of a
chromosomal segment.
INVERSION
• Inversion: a segment that has become
separated from the chromosome is
reinserted at the same place but in reverse
order
CHROMOSOMAL
TRANSLOCATION
A chromosomal segment is
removed from one chromosome
and inserted on another
chromosome
NONDISJUNCTION
• Chromosomes FAIL TO SEPARATE
correctly during meiosis
NONDISJUNCTION
• Produces gametes (and therefore a
baby) with one missing chromosome
or one extra chromosome
NONDISJUNCTION (IN MEIOSIS II)
FERTILIZATION
NONDISJUNCTION
• Every cell in that baby’s body will have __
copies of this chromosome instead of___.
• This condition is called ____________.
• Trisomy 21 = Individual has _____ copies of
chromosome # ________
NONDISJUNCTION
• Every cell in that baby’s body will have 3 copies
of this chromosome instead of 2.
• This condition is called __________.
• Trisomy 21 = Individual has _____ copies of
chromosome # ________
NONDISJUNCTION
• Every cell in that baby’s body will have 3 copies
of this chromosome instead of 2.
• This condition is called TRISOMY
• Trisomy 21 = Individual has __ copies of
chromosome # ____.
NONDISJUNCTION
• Every cell in that baby’s body will have 3 copies
of this chromosome instead of 2.
• This condition is called TRISOMY
• Trisomy 21 = Individual has 3 copies of
chromosome # 21.
TRISOMY 21 - DOWN SYNDROME
KARYOTYPES
• A picture of chromosomes in the body.
• Chromosomes pairs 1-22 are called
autosomes
• Chromosome pair 23 are called the sex
chromosomes
• Due to
nondisjunction
• Chromosome
makeup is XXY
• Creates a sterile
male
KLINEFELTER’S
SYNDROME
TURNER’S SYNDROME
• Due to nondisjunction
• Monosomy- the condition in which there is a missing
chromosome.
• Sex chromosome make up is X only
• Females that will not undergo puberty.
EDWARD’S SYNDROME
• Due to nondisjunction
• Extra number 18
chromosome (trisomy
18)
• Traits: Low ears,
kidney and heart
defects
PATAU’S SYNDROME
• Extra number 13 chromosome (trisomy 13)
• Traits: Deformed eyes, ears and lips
KEY POINT #1
Too much or too little DNA is bad!