Download Mutations

Mutations
Mutations are defined as “a sudden
genetic change in the DNA sequence
that affects genetic information”.
They can occur at the molecular level
(genes) and change a single gene, or at
the chromosome level and affect many
genes.
Things that can cause mutations are
called “mutagens”.
Known mutagens are ultraviolet light,
cigarette smoking, certain chemicals
like PCB’s.
Effects of Mutations
Silent mutations - have no effect on the
expression of the gene.
Causes for this type of mutation:
It is in a non-coding region
It does not change the amino acid sequence
The change does not affect the folding of the
protein
Inheritability of Mutations
It depends on where it occurs
i. Germ mutations – occur in gametes.
Inheritable (colorblindness, hemophilia)
ii. Somatic mutations – affect body cell, not
inheritable (cancer)
Types of Mutations – mistakes
a) Gene (point) Mutations – effects a
single gene
i. Substitution
ii. Frameshift
a) Chromosomal mutations – most
drastic, change in structure or # of
chromosomes (affects many genes)
III.
Point Mutations
a) Substitution – one base exchanges
for another, affects 1 amino acid
(Ex. GCA-TCA  GCT-TCA
Effects of substitution mutations
Missense mutations – causes a
change in the amino acid coded for
Nonsense mutations – causes a stop
codon to occur prematurely
a) Frameshift – affects several amino
acids
-Insertion – 1 base is inserted,
affects several amino acids
Ex. (GCA-TCA  GCA-GTC-A
-Deletion – base is removed, affects
several amino acids
Ex. (GCA-TCA  GCT-CA
Chromosome mutations
Nondisjunction – incomplete
chromosome division during
meiosis; results in gametes
with too many or too few
chromosomes.
Ex: Down syndrome is caused
by an extra #21 chromosome
Polyploidy
Aneuploidy
Down’s Syndrome
•Trisomy 21
•1 in 700 births
•Mental
retardation
•Males are sterile
but females are
not
Likelihood of chromosomal
mutations
1 in 1700 for mothers <
20.
1 in 1400 for mothers
>20<30.
1 in 750 for mothers
>30<35.
1 in 16 for mothers >45.
Sex chromosome disorders –
occurs as a result of nondisjunction
of the sex chromosomes
Ex: Turner’s syndrome – X-;
Klinefelter’s syndrome – XXY.
Klinefelter’s Syndrome
•XXY
•1 in 1,000
•Usually sterile because of
low sperm count
•Tall, sparse body hair
•Suffer from gynecomastiamale breast tissue
•Testosterone treatments
Turner’s Syndrome
•XO genotype—Monosomy X
•1 in 2,500 births
•Short, sterile
•75% result in non-disjunction
from the father
Other Chromosomal Mutations
 Affect many different genes
 Caused by errors in meiosis or environmental
disturbances
Translocation – occurs when a
piece of one chromosome
breaks off and attaches to a
nonhomologous chromosome
Inversion – occurs when a
piece of one chromosome
breaks off, flips, and reattaches
to the same chromosome
Deletion – occurs when a
piece of a chromosome
breaks off and is lost
Duplication – occurs when
a segment of a
chromosome is repeated
XYY-Jacob’s Syndrome a.k.a.
“Super Males”
• 1 in 1,000 men
•Normal appearance, very
tall
•Low IQ, prone to
violence