Download Genetic Mutations

Genetic Mutations
Mutations
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New inherited traits, or mutations, may appear in a
strain of plant or animal.
The first individual
showing the new trait is
called a mutant.
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2 Types of Mutations
Chromosomal mutations
 an abnormal change in the structure of all or part of a
chromosome or in the number of chromosomes an
organism has.
2 Types of Mutations
Gene mutations
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a change that affects a gene on a chromosome
For a mutation to be inherited it must be present in the
DNA of a gamete. The mutation must occur in a
gamete or in any cell from which a gamete develops.
Cannot be transmitted from body (somatic) cells.
How Mutations Happen
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Mutations occur naturally at a low rate. They are usually
the result of random errors in replication of the DNA.
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If environmental factors cause a mutation, the factor is
called a mutagen. (eg x-rays, UV light)
Mutation from UV Light
Chromosomal Mutations
Three kinds:
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1. Changes in Chromosome Structure
Chromosome structure may become permanently altered
during meiosis when chromatids become entangled and
their parts rearranged. (not same as crossing over)
Types of Changes in Chromosomal
Structure
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Four types:
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Translocation – transfer of a part of a chromosome to a
nonhomologous chromosome
Inversion – piece of the chromosome is rotated which reverses the
order of genes
Addition – piece of a chromosome breaks off and attaches to a
homologous chromosome which causes some genes to be repeated
Deletion – piece of the chromosome breaks off resulting in a loss of
some genes.
Mutations from X-Rays
Chromosomal Addition Syndrome
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Fragile X syndrome is caused when a spot on the X
chromosome contains a stretch of nucleotides in which a
small part of the chormosome is repeated (as many as
400 times). This causes a constriction in the x
chromosome making it quite fragile. Males who inherit
this X chromosome are mentally retarded. Females are
only mildly affected.
Chromosomal Mutations
Three kinds:
2) Nondisjunction
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The addition or loss of a whole chromosome.
Happens when chromosomes that normally separate during
meiosis remain together.
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Non-Disjunction Types
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Monosomy refers to a condition in which there is one
chromosome is missing. It is abbreviated 2N - 1. For
example, monosomy X is a condition in which cells have
only one X chromosome.
A trisomy has one extra chromosome and is
abbreviated 2N + 1. Trisomy 21 is an example of a trisomy
in which cells have an extra chromosome 21.
Non-Disjunction Types
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Monosomies and trisomies usually result from
nondisjunction during meiosis but can also occur in
mitosis. They are more common in meiosis 1 than meiosis
2.
They are generally lethal except monosomy X (female
with one X chromosome) and trisomy 21 (Down’s
Syndrome).
Affected individuals have a distinctive set of physical and
mental characteristics called a syndrome. For example,
trisomy 21 is Down syndrome.
Some common chromosomal abnormalities
are listed below.
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Abnormality
Down Syndrome
Turner Syndrome
Triple-X Syndrome
Klinefelter Syndrome
Jacob Syndrome
Karyotype
Trisomy 21
X
XXX
XXY
XYY
Karyotypes
Down Syndrome
Karyotype
Turner Syndrome Karyotype
Triple X Syndrome
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Triple X syndrome, also called trisomy X or 47,XXX, is
characterized by the presence of an additional X chromosome
in each of a female's cells. Although females with this condition
may be taller than average, this chromosomal change typically
causes no unusual physical features. Most females with triple X
syndrome have normal sexual development and are able to
conceive children.
Triple X syndrome is associated with an increased risk of
learning disabilities and delayed development of speech and
language skills. Delayed development of motor skills (such as
sitting and walking), weak muscle tone (hypotonia), and
behavioral and emotional difficulties are also possible, but these
characteristics vary widely among affected girls and women.
Seizures or kidney abnormalities occur in about 10 percent of
affected females.
Triple X Syndrome Karyotype
Klinefelter Syndrome
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Klinefelter's syndrome, 47, XXY, or XXY
syndrome is a condition in which human males have an
extra X chromosome.
The condition exists in roughly 1 out of every 1,000
males. One in every 500 males has an extra X
chromosome but does not have the syndrome.
The principal effects are development of small testicles
and reduced fertility. A variety of other physical and
behavioral differences and problems are common, though
severity varies and many boys and men with the condition
have few detectable symptoms.
Klinefelter Syndrome Karyotype
Jacob Syndrome
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Jacob's syndrome is a rare chromosomal disorder that
affects males.
Males with Jacob's syndrome, also called XYY males.
Jacob's syndrome occurs when a male inherits two Y
chromosomes from his father instead of one.
There are many symptoms associated with Jacob's
Syndrome. The most common symptoms are:
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learning problems at school
delayed emotional maturity
Males with Jacob’s syndrome are tall, thin, have acne,
speech problems, and reading problems.
Jacob Syndrome Karyotype
Turner Syndrome
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Turner syndrome is caused by monosomy X (absence of an
entire sex chromosome).
Occurring in 1 in 2000 – 1 in 5000 females, the syndrome has a
number of varied side effects. There are characteristic physical
abnormalities, such as ‘short stature, swelling, broad chest, low
hairline, low-set ears, and webbed necks.
Girls with Turner syndrome typically experience non-working
ovaries, which results in an absence of menstrual cycle and
sterility. Other health concerns are also frequently present,
including ‘congenital heart disease, hypothyroidism, diabetes,
vision problems, hearing concerns, and many autoimmune
diseases.
Cognitive deficits that are common with particular difficulties
in visuospatial, mathematical, and memory areas.
Non-Disjunction Types
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3) Polyploidy
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Cells have some multiple of the chromosome number.
Happens when chromosomes do not separate normally during
mitosis or meiosis.
Euploidy is the condition of having an exact multiple of the
haploid number
Aneuploidy is the condition where the chromosome number
is not an exact multiple of the normal haploid set