Download Notes: Mutations

Notes:
Mutations
13-3
GPS Standard
• SB2d. Describe the relationship between
changes in DNA and potential appearance of
new traits including:
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Alteration during replication:
Insertions
Deletions
Substitutions
• Mutagenic factors that can alter DNA.
– High energy radiation (x-rays and ultraviolet)
– Chemical
What are mutations?
• Sometimes cells can make
mistakes when copying
their DNA. These mistakes
are called mutations.
• Mutations- are changes in
the DNA sequence that
affects the genetic
information
• Mutations that occur in sex
cells can be inherited.
Gene Mutations
• Are mutations that affect one single gene or
protein.
• There are two types of gene mutations:
point and frameshift
Point Mutations
• Point Mutations occur at one nucleoltide and
only affect one amino acid.
– Ex: Substitution- one nucleotide is substituted for
another one
– this may or may not change the resulting amino
acid
Frameshift Mutations
• Frameshift mutations occur when a
nucleotide is added or deleted. This affects
every amino acid that comes after the
mutation.
– This will alter the protein so that it does not carry
out its normal function
Frameshift Mutations
• Ribosomes read in 3 letter codons
• THE FAT CAT ATE THE RAT
• Look how the ribosome would read this
sentence if the “H” in the first “the” was
deleted.
• TEF ATC ATA TET HER AT
Chromosomal Mutations
• Chromosomal Mutations- Changes in the
number or structure of chromosomes
• These are much worse than single gene
mutations (because it affects lots of genes)
• Deletion
– Occurs when part of a
chromosome is missing
or lost
• Duplication
– Occurs when part of
the chromosome is
repeated or doubled
• Inversion
– Occurs when the parts of
the chromosome are
reversed
• Translocation
– Occurs when two
chromosomes exchange
parts (one chromosome
breaks off and attaches to
another)
Mutagens
• Mutagens are chemical or physical agents in
the environment that may cause mutations.
– Examples: pesticides, tobacco smoke,
environmental pollutants, x-rays, uv light.
Effects of Mutations
• Some or most have no effect- they are
considered neutral
• some have a negative effect
– Can result in genetic disorders (like sickle cell)
– Can result in cancer
Effects of mutations
• Some have a positive effect
– Altered proteins may help organism in
changing environments
• Insects- may help them gain resistance to
insecticides
• Humans- may increase bone density
• Plants- Polyploidy (extra sets of chromosomes
makes the plants larger and stronger)
Mutations are important to evolution
• Mutations are the source of genetic
variability
• Mutations that occur in the gametes
(sex cells) are really important
– Are passed on to the next generation
– Affect the gene that the mutation
occurred in