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GENE MUTATIONS
MUTATIONS

Any mistake or change in the DNA sequence
POINT (MISSENSE) MUTATIONS

A change in a single base pair in DNA
 Example:
a single letter changed; the whole
meaning of the sentence changed
 THE
DOG BIT THE CAT.
 THE DOG BIT THE CAR.
FRAMESHIFT MUTATIONS

A single base is added or deleted from DNA
 The
mRNA strand would be out of position by one
base and every codon after that base would be
different.
CHROMOSOMAL MUTATIONS
Parts of chromosomes broken off or lost during
mitosis or meiosis
 Break and rejoin incorrectly

EFFECTS OF CHROMOSOMAL MUTATIONS




Occur mostly in plants
Gametes that should have a complete
set of genes may end up with extra
copies of some genes or completely
lack others
Few chromosome mutations are
passed on to the next generation
because they zygote usually dies
Deletions, insertions, inversions, and
translocations
ERRORS IN DISJUNCTION
Nondisjunction= the failure of
homologous chromosomes to
separate properly during meiosis
 one gamete has an extra
chromosome and the other is
missing a chromosome


Trisomy= when a gamete with an
extra chromosome is fertilized by a
normal gamete, the zygote will have
an extra chromosome
 47
chromosomes= Down syndrome

Triploidy- a total lack of separation of
homologous chromosomes; a gamete inherits a
complete set of chromosomes; offspring have
three sets of chromsomes and are triploid
 Happens
sterile
often in plants—tend to be larger and are

Monosomy- zygote lacks a chromosome
 human
females with a single X chromosome (Turner
Syndrome)
CAUSES OF MUTATIONS
Generally random events “spontaneous
mutations”
 Many environmental agents cause mutation

 Exposure
to x-rays, ultraviolet light, radioactive
substances, or certain chemicals
Often result in sterility or lack of normal
development; birth defects
 If they occur in body cells, they can cause
cancer
