Download Mutations

MUTATIONS
SC STANDARD B-4.9: The student will
exemplify ways in which new characteristics are
introduced into an organism or a population
Cornell Notes
Page 110
Topic: Mutations
Essential Question: What is a mutation, how do
mutations allow a species to change over time?
Mutation: The Basis of Genetic Change
A mutation is a change in the structure or
amount of genetic material of an organism
In general, genetic differences among
organisms originated as some kind of genetic
mutation.
Causes of Mutations
Occur naturally as accidental changes in
DNA or chromosomes
repair enzymes “overlook” errors
Rate of mutation can be accelerated by
some environmental factors called mutagens
forms of radiation
chemicals
Effects of Mutations
Depends on where and when mutations
occur
Germ Cell mutations
passed on to offspring
Somatic Cell Mutations
not passed on to offspring
could result in
• Normal tissue
• Cancer
Kind of Mutations
1. Mutations as changes in DNA
1. Point Mutation
1. change of a single nucleotide from 1 base to another
2. Insertion or Deletion
1. single nucleotide in a sequence added or dropped
1. rare
Point Mutation
Insertion or Deletion
Mutations as Changes in Results of Genes
1. Silent Mutations
1. has no effect on gene’s function
2. frequently happens because genetic code is
redundant
Mutations as Changes in Results of Genes
2. Missense or Replacement Mutations
codon changed so results in a different
amino acid
Mutations as Changes in Results of Genes
3. Frameshift Mutations
“reading frame” of a codon depends on the
starting point
insertions or deletions may shift the reading
frame which may cause the remaining
sequence of nucleotides to be “read” as
different codons
Frameshift Mutations
Mutations as Changes in Results of Genes
4. Nonsense Mutation
results when a codon is changed from an
amino acid to a “stop” signal
- resulting protein will be cut short & may
fail to function
Nonsense Mutation
Mutations
5. More or Fewer Amino Acids
if an insertion or deletion is a multiple of 3
the resulting protein will have fewer or
more amino acids
the more codons that are inserted or deleted
the more likely the resulting protein will be
malfunctioning
Chromosomal Mutations
In eukaryotic cells, the process of meiosis
creates the chance of mutations at the
chromosomal level:
 involve changing the location of genes on
chromosomes, or the numbers of copies of some
genes
4 Types of Chromosomal Mutations
 1. Deletions
 2. Duplications
Involve loss of all or a
Produce extra copies
part of a
of parts of a
chromosome
chromosome
 3. Inversions
Reverse the direction
of parts of
chromosomes
 4. Translocations
Occur when a part of
one chromosome
breaks off &
reattaches on the end
of another
chromosome
Trisomies
 3 copies of a
chromosome, in whole
or in part
 seen in several
different
chromosomes
 most commonly in
chromosome 21
Karyotype of Trisomy 21
Significance of Mutations
1. Neutral
1. most mutations
2. Lethal or Harmful
1. resulting proteins
defective, disrupt
normal activity
3. Beneficial
1. new altered protein
offers individual
advantages
 Somatic cell mutations:
affect individual only
 Germ Cell mutations
passed on to offspring
Basis for new genetic
variation in population
Polyploidy
condition in which organism has extra sets of
chromosomes (due to failure in meiosis)
Polyploidy plants often hardier, larger than diploid
plants
Animations
http://highered.mheducation.com/sites/007
2556781/student_view0/chapter11/animati
on
http://www.dnatube.com/video/685/DNA-Duplication-and-Mutations