Mutations for ap bio
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Transcript of Mutations for ap bio
![Page 1: Mutations for ap bio](https://reader031.fdocuments.us/reader031/viewer/2022022419/5883ce901a28abb7308b609d/html5/thumbnails/1.jpg)
Mutations all
AP Students
need to know
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Mutations caused by
whole/part chromosomes
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Chromosomal mutations
• In nondisjunction, pairs of homologous chromosomes do not separate normally during meiosis
• As a result, one gamete receives two of the same type of chromosome, and another gamete receives no copy
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Having an abnormal number of
chromosomes is a condition known
as aneuploidy
Having 3 copies of a particular
chromosome is called a trisomy
Having 1 copy of a particular
chromosome is called a monosomy
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Polyploidy is a
condition in which
an organism has
more than two
complete sets of
chromosomes
Recent research
has shown that
this Chilean
rodent is a
tetraploid
Very rare among
animals
Common in plants,
some fish, some
amphibians
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Polyploidy - having more than two complete chromosome sets The normal state is having 2 of each chromosome
(homologous pairs) When organisms have 3 or 4 of each chromosome, that is
called polyploidy Triploidy (3n), tetraloidy (4n), hexploid (6n), octapolid (8n)
Very uncommon in animals Some fish and amphibians, mostly
Quite common in plants
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Down
Syndrome
Caused by a trisomy of chromosome 21
1/700 births in US
The result of nondisjunction during meiosis I
Risk increases with the age of the mother
Mental retardation, increased risk of other diseases, shortened
life span, underdeveloped and likely sterile
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Trisomy 18 – Edward’s syndrome low birth
weight, mental retardation, extra fingers and toes
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Trisomy of sex
chromosomes
• Klinefeltersyndrome is the result of an extra chromosome in a male, producing XXY individuals
• Monosomy X, called Turner syndrome, produces X0 females, who are sterile; it is the only known viable monosomy in humans
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Quick Think
Gene dosage, the number of active
copies of a gene, is important to
proper development.
Identify and describe two disorders
that are the result of improper gene
dosage
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Alterations of Chromosome Structure Chromosomal mutations
include
Deletion
Inversion
Duplication
Translocation
Often occur during meiosis
Chromosomes break &
rejoin incorrectly
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Deletion mutations
A piece of chromosome is lost during meiosis
Cri du chat is one condition that results -distinctive cry, severe retardation, shortened life span
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Inversion Mutations
A double break where the piece reattaches, but backwards
Hemophilia is a inversion on the X chromosome
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Duplication mutation
A piece breaks off from one chromosome and reattaches to the sister chromatid
Fragile X syndrome is caused by this, 2nd most common form of mental retardation after Downs syndrome
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Translocation mutation
A piece breaks off one chromosome and
reattaches to a different chromosome
Burkitt’s lymphoma is caused by this
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Sex-linked mutations in
humans
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Colorblindness Colorblindness
Recessive
X chromosome
Men are more likely to be colorblind than women…WHY
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Hemophilia
Recessive, X-linked
Prolonged bleeding when injured
Clots slow to form
Caused by a mutation for a gene on
the X chromosome that codes for a blood clotting
protein
Can be treated but not cured
Bleeding
(bruising) after an
injection
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Duchenne muscular
dystrophy
Recessive, X-linked
1/3500 males in US
Progressive weakening of
muscles
Loss of coordination
Death by early 20s
Mutation in the gene that codes
for a muscle protein (dystrophin)
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Point MutationsSmall changes in the DNA
sequence
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Point Mutations
point mutation = a change in a single base pair in a gene
They can have catastrophic consequences, or none at all
3 main types:
Substitution
Insertion
Deletion
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Substitution mutations
A base pair is replaced with a different base pair
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Substitution Think of it like a sentence:
Normal sentence would read THE DOG BIT THE CAT
A point mutation might make the sentence read: THE DOG BIT THE CAR
This changes the meaning of the sentence, but not dramatically.
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Example: sickle cell anemia
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Advantages of sickle cell AA – no sickle cell, susceptible to the worst effects of
malaria
Aa – no sickle cell, but call pass recessive allele to
offspring, some protection from malaria
aa – sickle cell disease
This is called The Heterozygote Advantage
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Changing a single
base may not cause
any change at all:
The changed base may
still code for the same
amino acid
Proline is coded for by
CCC, CCA, CCG, and
CCU,
This is called a silent
mutation
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Insertions & Deletions
•Insertion - add extra letters
•Deletions – delete letters
•called frameshift mutations
• The 3 letter reading frame is
shifted
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Frameshift Mutations Think of it as a sentence again:
THE DOG BIT THE CAT
Adding an extra letter makes it: THH EDO GBI TTH ECA T
It changes the entire sentence to nonsense. This kind of mutation has a more dramatic effect on the DNA sequence and is usually lethal
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1.
2.
3.
What kind of mutation is represented
by 1, 2, and 3?
Will mutation 1 affect the resulting
protein?
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Tay-Sachs Frame shift mutation – 4 added nucleotides (insertion)
Autosomal, recessive
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Cystic Fibrosis Deletion frameshift mutation – 3 missing letters,
autosomal recessive
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Breast/Ovarian Cancer BRCA I and BRCA II – usually a deletion mutation
Autosomal dominant
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Huntington’s Disease Autosomal dominant
>37 CAG repeats on the short arm of chromosome 4