MUTATIONS
Term
Chrom-some; somaHomo-logKaryo-
Meaning
Example
A _____________________ is a _____________________ change in the DNA sequence of a
gene. Sometimes mutations in DNA can cause changes in the way a cell behaves. This is because
genes contain the _____________________ necessary for a cell to work. If some of the
instructions to the cell are wrong, then the cell may not know what it is supposed to do!
THE EFFECT OF MUTATIONS
It is not correct to assume that all mutations are _____________________. There are many
documented cases where a mutation has helped an organism _____________________. These
___________________________ occur mostly in viruses and bacteria, but sometimes occur in
multicellular organisms as well. Sometimes a mutation may be _____________________; that
is, it causes a change in trait, but does not help or hinder the organism. Additionally, a mutation
may occur that does not change the trait at all. These are known as
_____________________________.
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TWO MAIN TYPES OF MUTATIONS
1. ______ mutations- affect the DNA strand itself
2. __________________ mutations- affect or involve the chromosomes
GENE MUTATIONS
HOW DO MUTATIONS OCCUR?
There are two ways in which DNA can become mutated:
1. Mutations can be _____________________. This happens when environmental agents
damage DNA, or when mistakes occur when a cell copies its DNA prior to cell division.
2. Mutations can be _____________________. This means that if a parent has a mutation in
his or her DNA, then the mutation is passed on to his or her children.
Types of mutations that can occur during DNA replication
During DNA replication, mistakes occur during the copying process. The diagram below shows
a normal, non-mutated replication event.
_____________________ mutation. A substitution mutation occurs when one nitrogenous base
is replaced with a different one.
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_____________________ mutations
_____________________ mutation. An insertion mutation occurs when an extra nucleotide is
added to the sequence. This will change the “reading frame”, and likely result in a change in all
amino acids downstream from the mutation.
_____________________ mutation. A deletion mutation occurs when a nucleotide is omitted
from the sequence. Like the insertion mutation, this will change the “reading frame”, and likely
result in a change in all amino acids downstream from the mutation.
CHROMOSOME MUTATIONS
_____________________ mutations only occur during _____________________. They involve
the rearrangement of entire blocks of genes, rather than just a few individual bases within a gene.
_____________________ mutation. A break may occur at
two points on the chromosome and the middle piece of the
chromosome falls out. The two ends then rejoin to form a
chromosome lacking some genes. Alternatively, the end of a
chromosome may break off and be lost.
_____________________ mutation. An interior piece of
chromosome falls out, rotates 180°, then rejoins. There is no
loss of genetic material. The genes will be in reverse order.
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_____________________. A group of genes moves to a different
chromosome. The two chromosomes are different types. This will
cause major problems during sperm or egg formation. Some
gametes will receive extra genes, while others will not receive
enough. This could be problematic if these gametes go through
fertilization.
_____________________. A segment is lost from one
chromosome and is added to another, similar chromosome. Some
gametes will receive double the genes while others will have
none. This could be problematic if these gametes go through
fertilization.
ANEUPLOIDY
_____________________ is a type of chromosomal mutation in
which an individual inherits more or fewer chromosomes than normal. In some cases, this will
result in miscarriage during pregnancy. In other cases, the organism may live and survive.
___________________________ is an example of aneuploidy. In Down syndrome, the
individual inherits an extra chromosome ______. Thus, the individual has ______ of that type of
chromosome, giving that individual a total of ______ chromosomes. This type of chromosomal
mutation is most common with the ______ chromosomes.
_____________________ syndrome- Extra chromosome ______- decreased cognitive ability, poor muscle
tone, heart defects, certain facial characteristics
____________________ syndrome- Extra chromosome ______- internal organ defects, high miscarriage rate
___________________ syndrome- Extra chromosome _____- mental and motor abnormalities, polydactylism
_________________ syndrome- Extra chromosome ______- mental abnormalities, musculoskeletal and
neural abnormalities
_____________________ syndrome- Extra chromosome ______- eye has appearance of a cat eye
___________________ syndrome- _____- female; typically sterile, ADHD and learning disabilities common
_____________________ syndrome- ______- male; small testicles, sterile, very common (1/500-1/1000),
learning disabilities are common, may have increased breast tissue. XXYY is a variation of this disorder, with more
severe mental and learning disabilities. XXXXY is another variation.
________________ syndrome- ___- female; can be infertile, behavioral and learning disabilities are common;
typically, these females are asymptomatic and go undiagnosed. XXXX and XXXXX are more severe variations.
______ syndrome- male; common (1/1000), usually asymptomatic and undiagnosed, higher incidence of
behavioral and learning disorders.
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