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Mutations
12-4
Mutation
 Now and then cells make mistakes in
copying their own DNA


They can insert an incorrect base
or skip a base as the new strand is put
together.
 Mistakes are called mutations
Mutation
 Latin word meaning “to change.”
 Mutations are changes in the genetic
material.
 There are 2 types of mutations: gene
and chromosomal
Gene Mutations
 Gene mutations involving changes in
one or a few nucleotides are known as
point mutations

Include: substitutions
 Insertions
 Deletions
 If a nucleotide is added or deleted, groupings
are shifted for every codon that follows
 Changes like these are called frameshift
mutations


Shifts reading frame of genetic message
May change every amino acid that follows
mutation
Chromosomal Mutations
 Chromosomal mutations involve
changes in the number or structure of
chromosomes
 They may change the locations of genes
on chromosomes, and may even change
the number of copies of some genes.
 Deletions – loss of all or part of a
chromosome
 Duplications – extra copies of parts of a
chromosome
 Inversions – reverse direction of parts of
chromosomes
 Translocations – part of a chromosome
breaks off and attaches to another
Significance of Mutations
 Many mutations are neutral having little
or no effect.
 Mutations that cause major changes in
proteins are often harmful

producing defective proteins that disrupt
normal biological activities.
Significance of Mutations
 Mutations are also the source of genetic
variability in a species.
 Some of this variation may be highly
beneficial.
 Harmful mutations are the causes of many
genetic disorders
 Harmful mutations are also associated with
many types of cancer.
 Beneficial mutations may produce proteins
with new or altered activities

can be useful to organisms in different or
changing environments.
Polyploidy
 Plant and animal breeders often take
advantage of beneficial mutations.

when a complete set of chromosomes fails to
separate during meiosis, the gametes that result
may produce triploid (3N) or tetraploid (4N)
organisms.

The condition in which an organism has extra
sets of chromosomes is called polyploidy.
Polyploidy

Polyploid plants are often larger and stronger
than diploid plants.

Important crop plants have been produced in
this way, including bananas and many citrus
fruits.