Mutations are changes in the nucleotide sequence of DNA that can occur in somatic or germ cells. Most mutations are neutral or repaired by enzymes, but some can be harmful, like causing cancer, or beneficial by improving survival. There are two main types of mutations: chromosome mutations, which involve changes to chromosomes like deletions, inversions, duplications, and translocations; and gene mutations, which change the nucleotide sequence of genes, such as point mutations, insertions, deletions, and frameshift mutations. The rate of mutations depends on factors like the frequency of primary DNA changes, the probability of repair, and the probability that a mutation can be recognized.
2. What Are Mutations?
• Changes in the
nucleotide sequence of
DNA
• May occur in somatic
cells (aren’t passed to
offspring)
• May occur in gametes
(eggs & sperm) and be
passed to offspring
3. Are Mutations Helpful or
Harmful?
• Mutations happen
regularly
• Almost all mutations are
neutral
• Chemicals & UV
radiation cause
mutations
• Many mutations are
repaired by enzymes
4. Are Mutations Helpful or
Harmful?
• Some type of skin
cancers and leukemia
result from somatic
mutations
• Some mutations may
improve an organism’s
survival (beneficial)
13. Nondisjunction
• Failure of chromosomes to
separate during meiosis
• Causes gamete to have too many
or too few chromosomes
• Disorders:
– Down Syndrome – three 21st
chromosomes
– Turner Syndrome – single X chromosome
– Klinefelter’s Syndrome – XXY
chromosomes
17. Gene Mutations
• Change in the
nucleotide sequence
of a gene
• May only involve a
single nucleotide
• May be due to
copying errors,
chemicals, viruses,
etc.
18. Types of Gene Mutations
• Include:
– Point Mutations
– Substitutions
– Insertions
– Deletions
– Frameshift
19. Point Mutation
• Change of a single
nucleotide
• Includes the
deletion, insertion, or
substitution of ONE
nucleotide in a gene
20. Point Mutation
• Sickle Cell
disease is the
result of one
nucleotide
substitution
• Occurs in the
hemoglobin gene
21. Frameshift Mutation
• Inserting or deleting
one or more
nucleotides
• Changes the “reading
frame” like changing a
sentence
• Proteins built
incorrectly
23. Factors affecting rate of mutation
• 1: FREQUENCY OF PRIMARY CHANGES IN DNA
The mutation rate depends on the frequency of primary
changes in DNA. These primary changes may arise from
spontaneous molecular changes in the DNA, or be induced
by chemical or physical agents in the environment.
• 2: PROBABILITY OF REPAIR
The second influential factor is the probability that, when a
change in DNA takes place, it will be repaired. Most cells
posses a number of mechanisms to repair changes in DNA,
so most alterations are repaired before they are replicated.
• If these repair systems are effective, mutation rates will be
low. If they are faulty, mutation rates will be increased. There
are even mutation that increase the overall mutation rate for
other genes. Such mutations usually occur in genes that
encode components of the repair mechanisms or
repair enzymes.
•
24. • 3: PROBABILITY OF RECOGNITION
The third factor is one that influences the ability to
calculate mutation rates. It is the probability that a
mutation is recognized and recorded. When DNA is
sequenced, all mutations are potentially detectable.
In practice, however, sequencing is still quite
expensive, so most mutations are detected by their
phenotypic effects. Some mutations may appear
more likely to take place simply because they are
easier to detect.
