Download mutations that affect an entire chromosomes Chromosomal

Mutations
KEY CONCEPT
Mutations are changes in DNA that may or may not
affect phenotype.
Mutations
Some mutations affect a single gene, while others affect
an entire chromosome.
• Many kinds of mutations can occur, especially during
replication.
• A mutation is a change in an organism’s DNA.
Mutations
Gene mutation: mutations that affect a single genes
• Point mutation-substitutes one nucleotide for
another
mutated
base
Mutations
More about gene mutations…
• Frameshift mutation- inserts or deletes a
nucleotide in the DNA sequence.
Mutations
Chromosomal Mutations: mutations that affect an entire
chromosomes
• Chromosomal mutations may occur during crossing over
– Chromosomal mutations affect many genes.
– Gene duplication results from unequal crossing over.
Mutations
• More about chromosomal mutations…
• Translocation results from the exchange of DNA
segments between nonhomologous
chromosomes.
Mutations
Potential impact: Chromosomal mutations typically have a
large effect on an organism; may result in a disrupted gene
or abnormal regulation of genes
• Mutations may or may not affect
phenotype
• Point mutations may result in
premature stop codons or amino
acids with very different properties
from the correct amino acid…
• May disrupt a splice site
• May disrupt a regulatory DNA
sequence
• Frame mutations may result in a
completely altered protein or a
premature stop codon
blockage
no blockage
Mutations
Silent: some mutations have no apparent effect
• A point mutation may not change the amino acid that is
coded for
• Even if a change occurs, the change may be in an intron
that is removed & this has no effect
• A change may not significantly affect the function of a
protein if the new amino acid is similar to the correct one
or occurs away from the active site or does not influence
protein structure
Mutations
Mutagens: agents in the environment that can change DNA
• Replication errors can cause
mutations.
• Mutagens, such as UV ray and
chemicals, can cause
mutations.
• Some cancer drugs use
mutagenic properties to kill
cancer cells.
Mutations
Summary Stuff:
• Mutations in body cells do not affect offspring.
• Mutations in sex cells can be harmful or beneficial to
offspring.
• Natural selection often removes mutant alleles from a
population when they are less adaptive.