Genetic Disorders Discussion
Bellwork: Copy the following pictures
and explain the direction that water
will move
Science Fact of the Day:
A crocodile's tongue attaches to the roof of its mouth.
CO:
LO:
Four things that cause mutations.
1) Errors in replication
2) Errors in transcription
3) Errors in cell division
4) External agents
Mutations can affect the reproductive cells
of an organism by changing the sequence
of nucleotides within a gene in a sperm or
an egg cell.
If this cell takes part in fertilization,
the altered gene would become part
of the genetic makeup of the
offspring.
The mutation may produce a new trait or it
may result in a protein that does not work
correctly.
Sometimes, the
mutation results
in a protein that
is nonfunctional,
and the embryo
may not survive.
In some rare
cases, a gene
mutation may
have positive
effects.
If the DNA of a nonreproductive cell is
changed, the
mutation would not
be passed on to
offspring.
However, the
mutation may cause
problems for the
individual.
Mutations that produce changes in whole
chromosomes are known as chromosomal mutations.
A karyotype is an
organized profile of a
person's chromosomes. In
a karyotype,
chromosomes are
arranged and numbered
by size, from largest to
smallest. This helps
scientists quickly identify
chromosomal changes
that may result in a
genetic disorder.
Few chromosomal mutations are passed on to
the next generation because the zygote
usually dies.
In cases where the zygote lives and develops,
the mature organism is often sterile and
thus incapable of producing offspring.
The 4 kinds of chromosomal mutations are: deletions,
duplications, inversions, and translocations.
Cri-du-chat
• Babies with the cry of the cat syndrome have a cry
which sounds like that of a cat in distress because the
infant’s larynx is improperly developed. Cri-du0chat
babies are severely mentally retarded and have a small
cranium. The incidences of this syndrome is 1 in
100,000 live births.
Caused by a partial deletion of chromosome 5
Polyploidy is a condition in which an organism has
extra sets of chromosomes.
Trisomy occurs when someone is born with three
copies of a chromosome. Down Syndrome is the
most common form of trisomy. In Down Syndrome,
chromosome 21 is tripled.
Down’s Syndrome
Trisomy 21, one of the most common causes of mental retardation is due to
an extra chromosome 2`. This results in a number of characteristic features,
such as short stature, broad hands, stubby fingers and toes, and a wide
rounded face. Individuals with this syndrome have a high incidence of heart
defects and lukemia. The average risk of having a child with Down’s
syndrome is 1 in 750 live births. Mothers in their early twenties have a risk of
1 in 1,500, women over 35 have a risk factor of 1 in 70.
Edward’s Syndrome
• Trisomy 18 produces
severe mental
retardation and a
highly characteristic
pattern of
malformations such as
elongated skull, a
narrow pelvis, rocker
bottom feet. Nearly
all babies born with
this syndrome die in
early infancy. The
frequency of this
syndrome is 1 in 5,000
live births.
Patau Syndrome
• This syndrome (trisomy 13)
causes severely abnormal
cerebral functions and
virtually always leads to
death in early infancy. This
baby has very pronounced
clefts of the lip and palate,
broad nose, small cranium
and nonfunctional eyes.
Heart defects and severe
mental retardation are also
part of the clinical picture.
The frequency is 1 in 15,000
live births.
Nondisjunction occurs when homologous
chromosomes do not separate. The result may be
abnormal numbers of chromosomes in the gametes.
Nondisjunction is the most common error in meiosis.
Turner Syndrome (XO)
• This is a result of
nondisjunction in
meiosis. These girls
appear normal
before puberty, but
as they grow
secondary sex
characteristics do not
develop and no ova
are produced. The
frequency of this
syndrome is 1 in
2,500 live births.
Klinefelter Syndrome (XXY)
• This is a result of
nondisjunction in
meiosis. The
frequency of this
condition is 1 in
1,000 live male
births.
Characteristics
include a tall stature
and sterility. Men
appear normal in
other ways.
Jacobs (XYY)
• A chromosome
aberration which is
caused by
nondisjunction of the Y
chromosome during
the second phase of
meiosis. Occurrence is
1 in 1,000 live male
births. Men with this
abnormality are tall
and have low mental
ability.
Triple X
• Occurs at a frequency
of 1 in 1,000 female
live births. No specific
abnormalities are
associated with this
condition. The vast
majority of women
with this condition
are normal mentally
and physically and are
fertile.
Genetic tests are now available for hundreds of
disorders making it possible to determine whether
prospective parents risk passing such genes to their
children.
DNA testing can pinpoint the exact genetic basis of a
disorder making it possible to develop more effective
treatment for individuals affected by genetic disease.
Beneficial mutations may produce proteins with new
or altered activities that can be useful to organisms in
different or changing environments.
Review Time
Meiosis
2 divisions
nucleus
start
Crossing over
DNA
fingerprint
Gel
electrophoresis
translation
Double helix
tRNA
2n
Diploid
protein
codon
23 pairs
Genetic code
uracil
polypeptide
mRNA
Trisomy 21
Codon chart
mutation
DNA
4 cells
N
nondisjunction
UCU
Haploid
gametes
ribosome
karyotype
transcription
mitosis
Amino acid
Genetic
variation
biology