Mutations Continued
KEY CONCEPT: Mutations are changes in DNA that may or may not affect phenotype.
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A mutation is a random change in an organism's genetic material
Heritable mutations can lead to changes in the gene pool of a population
New Mutations can be:
o Harmful
o Neutral
o Advantageous
SOME MUTATIONS AFFECT A SINGLE GEME, WHILE OTHERS AFFECT AN ENTIRE CHROMOSOME
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o A mutation is a change in an organism's DNA
o Many kinds of mutations can occur, especially during replication
o A point mutation substitutes one nucleotide for another
Many kinds of mutations can occur, especially during replication
o A frame shift mutation inserts or deletes a nucleotide in the DNA sequence
Chromosomal mutations affect many genes
Chromosomal mutations may occur during cross over
o Chromosomal mutations affect many genes
o Gene duplication results from unequal crossing over
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Translocation results from the exchange of DNA segments between non-homologous
chromosomes
MUTATIONS MAY OR MAY NOT AFFECT PHENOTYPE
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Chromosomal mutations tend to have a big affect
Some gene mutations change phenotype
o a mutation may cause a premature stop codon
o a mutation may change protein shape or the active site
o a mutation may change gene regulation
Some gene mutations do not affect phenotype
o A mutation may be silent
o A mutation may occur in a non coding region
o A mutation may not affect protein folding or the active site diff. sequence, same
shape, form follows function
Mutations in body cells do not affect offspring
Mutations in sex cells can be harmful or beneficial to offspring. These are evolutionary
significant
Natural selection often removes mutant alleles from a population when they are less adaptive
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BENEFICAL MUTATION EXAMPLE
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Tolerance to high cholesterol levels in humans
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in the small village of Limone, about 40 villagers have extraordinary high levels of
blood cholesterol, with no apparent harmful effect on their coronary arteries
o The village has a population of 980 inhabitants and was until recently largely isolated
from the rest of the world with sheer cliffs behind the village, the lake in front of them,
and no road access
The 40 villagers possess a point mutation which alters the protein produced by just one amino
acid. This protein is ten times more effective at mopping up excess cholesterol.
o No matter how much excess cholesterol is ingested, it can always be disposed of.
o All carriers of the mutation are related and have descended from one couple who
arrived in Limone in 1636
o Generally, the people of Limone live longer and chow a high resistance to heart
disease