Download Mutations - Choteau Schools

Chapter 11
DNA and Genes
Section 3
Genetic Changes
Mutations
A mutation is any change in the DNA
sequence.
Mutations can be caused by:
Errors in:
replication.
transcription.
cell division.
External agents.
Mutations in Reproductive Cells
The mutation occurs in the gamete and is
passed on to the zygote.
May be beneficial or harmful:
May result in a new trait which benefits the
organism or in structural or functional
problems in the cells or the organism.
At times, the problem is so severe that the
organism does not survive.
Mutations in Body Cells
DNA is changed by an outside force (such
as radiation).
This change may impair the function of
the cell.
The mutation is passed on to daughter
cells when the original cell divides.
Example: Cancer
Point Mutation
A change in a single base pair in DNA.
Can change the coding for amino acids,
which can result in a different protein.
Frameshift Mutation
Results when a single base is missing or
is added in DNA and is then transcribed
into mRNA.
Changes nearly every amino acid located
after the deletion or addition in the
protein.
Chromosomal Mutations
Can occur in a variety of manners:
Parts of the chromosome can be broken off
and lost during mitosis or meiosis.
The chromosome can break and rejoin
incorrectly (backward or to the wrong
sections).
Chromosomal Mutations
Very common in plants.
During meiosis the homologous
chromosomes will not pair correctly
when one chromosome has extra or
missing parts, resulting in incorrect
separation of the homologous
chromosomes, leaving one gamete with
too many chromosomes and the other
with not enough.
Chromosomal Mutations
Few chromosomal mutations are passed
on to the next generation because the
zygote usually does not survive.
In cases that the organism reaches maturity,
it is usually sterile.
Causes of Mutations
May be spontaneous
Simply occur.
Caused by mutagens
Any agent that can cause a change in DNA.
Examples: radiation (X-rays, UV rays, nuclear
radiation), chemicals (dioxins, asbestos,
benzene, formaldehyde), and high
temperatures.
Greater the exposure is to mutagens the more
likely it is that mutations will form.
Repairing DNA
Enzymes proofread the DNA and replace
incorrect nucleotides with correct
nucleotides.