Genetic Mutations
Mutations
• 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.
2 Types of Mutations
1) Chromosomal mutations
• An abnormal change in the structure
of all or part of a chromosome or in
the number of chromosomes an
organism has.
• For example, an organism can be
missing a part of a chromosome or
have 1 added to it’s total number.
2 Types of Mutations
2) Gene mutations
•A change that affects a
gene on a chromosome
•Example could be a gene
that creates a disease in an
organism.
How Mutations are Inherited
• 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
• Mutations occur naturally at a low rate.
They are usually the result of random
errors in replication of the DNA.
• This can account for differences in DNA of
identical twins, especially during gestation.
• If environmental factors cause a mutation,
the factor is called a mutagen. (eg x-rays,
UV light, food preservatives, food
colorings, etc.)
Mutation
from UV
Light
Chromosomal Mutations – 3
Kinds
• 1. Changes in Chromosome
Structure
• Chromosome structure may
become permanently altered
during meiosis when chromatids
become entangled and their
parts rearranged. (Not the same
as crossing over)
Types of Changes in Chromosomal
Structure
• Four types:
• Translocation – transfer of a part of a chromosome
to a non-homologous 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 XRays
Chromosomal Point Addition
Syndrome
• Fragile X syndrome is caused
when a spot on the X
chromosome contains a
stretch of nucleotides in
which a small part of the
chromosome 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 – 3 Kinds
2) Nondisjunction
• The addition or loss of a whole
chromosome.
• Happens when chromosomes that
normally separate during meiosis
remain together.
Interphase
Prophase I
Metaphase 1
Anaphase 1
Telophase 1
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2
Haploid Cells at the end of
Meiosis 2
Non-Disjunction Types
• 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.
• Trisomy refers to a condition in which there is 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
• 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:
• Abnormality
Karyotype
• Down Syndrome
Trisomy 21
• Turner Syndrome
X
• Triple-X Syndrome
XXX
• Klinefelter Syndrome
XXY
• Jacob Syndrome
XYY
Karyotypes
Down Syndrome Karyotype
Turner Syndrome Karyotype
Triple X Syndrome
• 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
• 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
• 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.
Klinefelter 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’s Syndrome
• 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.
Jacob’s Syndrome
• There are many symptoms associated with
Jacob's Syndrome. The most common
symptoms are:
• 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
• 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.
Turner Syndrome
• 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.
Down Syndrome Video
• http://www.youtube.com/watch?v=5M--xOyGUX4