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Warm-Up
• Write the amino acid and mRNA sequence
that would go along with the incomplete tRNA
molecules
• What other part of a cell would be directly
involved with the tRNA?
UAC
GGU
AAA
CGU
8.7 Mutations
Mutations can effect a single gene or
an entire chromosome
• Mutation- a change in an organism’s DNA
• Usually mutations that affect a single gene
happen during replication while one that
affects many genes or an entire chromosome
happen during meiosis (replication of
gametes- eggs and sperm)
Gene Mutations
• 2 types:
– Point mutation
• One nucleotide gets substituted for another
• Most often mistake is caught by DNA Polymerase but if
not, it will continue to be replicated
– Frameshift mutation
• Insertion or deletion of a nucleotide
• Generally has a worse effect on the protein than point
because it shifts the whole sequence
Example of Frameshift Mutations
• From page 252
• Consider this DNA nucleotide sequence:
THE CAT ATE THE RAT
• Now if you had a deletion of the E in the first THE,
look what happens:
THC ATA TET HER AT…
• What has happened to the reading frame? How
would this effect the mRNA strand (and therefore
the sequence of amino acids)?
Chromosomal Mutations
• Can result in duplicate or missing copies of entire
genes gene duplication/deletion
• Can result in a piece of one chromosome
connecting to a piece of a nonhomologous
chromosomes (a different chromosome, the
wrong one) gene translocation
*we will discuss chromosomal mutations in more detail after we talk about
meiosis
Mutations may or may not affect
phenotype
• Phenotype- physical characteristics
• Whether it affects it or not depends on number
of genes involved, location of the mutation,
function of gene etc
• Mutations that occur in body cells ONLY affect
that organism
• Mutations that occur in germ cells (eggs and
sperm) can affect offspring
– This is what creates genetic variation, the basis of
natural selection
What Causes Mutations?
• Natural replication errors missed by DNA
replication
– These accumulate over time (one major cause of
aging)
• Mutagens
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Agents in the environment that can change DNA
Can break DNA strands
Can speed up the rate of replication errors
Natural sources (like UV light) and chemicals (like
cigarettes)