Transcript Genetic Disorders - Mrs. Murchison's 8th Grade Science and

Genetic Disorders
Inherited in different ways

Gene mutations
Autosomal / Sex-linked
Dominant / recessive/ codominant

Chromosomal mutations
Too many- trisomy
Too few- monosomy
Deletions of large portions of the chromosome
 Autosomal Recessive
 Lack of enzyme
hexosaminidase A (hex A),
which breaks down fatty acids in
brain in nervous tissue
 Symptoms begin to appear at 46 months
 Developmental delay, loss of
motor skills and mental
functions, blindness, deafness,
paralysis, non-responsive to the
environment
 Death by 5 years
 Found primarily in those
descendants of Ashkenazi Jews

1/30 American Jews carry the
gene
 Autosomal recessive Chromosome #7 - Point
mutation stops production of a
protein in the lungs and
pancreas

Prevents cells from
transporting Cl- ions out of
the cell
 Lung Congestion



Abnormally thick mucus lining
in lungs
Chronic Bacterial Infections
(pneumonia)
Treated with antibiotics, lung
transplant, and new genetic
engineering treatments
 Northern European descent
Albinism
Autosomal recessive
On one of many genes
controlling pigment
production
Lack of pigment in the
skin, hair, and eyes
 Autosomal recessive- Chromosome #12
 Do not contain enzyme phenylalanine
hydroxlyase (PAH) that breaks down amino
acid phenylalanine into amino acid tyrosine



Phenylalanine builds up in brain
Toxic to central nervous system (CNS)
Learning Difficulties, seizures
 Tested at birth
 PKU – 1/10,000

U.S.  1/50 carry PKU allele
 Regulated by Strict diet


Low protein: no meat, eggs, dairy
No Aspartame: sugar substitute sold as Equal
or NutraSweet
 Contains amino acid phenylalanine – 50%
Achondroplasia
Autosomal dominant
1 of 6 kinds of Dwarfism
(each has different
characteristics
 Normal torso length with
shortened limbs
 Most common form of
dwarfism
 Homozygous dominant
zygotes will miscarry
 Autosomal Dominantchromosome #4
 Lethal due to
degeneration of brain
cells
 Symptoms onset around
ages 35-50
 Lose control over
muscles causing
uncontrolled
movements, loss of
intellectual faculties,
and emotional
disturbance
Hypercholesterolemia
Familial high cholesterol
Autosomal codominant
on Chromosome #19
Cells have reduced ability
to remove cholesterol
(lipids) from the blood
which causes a build up
in the arteries (called
atherosclerois)
Blockage leads to early
age heart attacks
Hypercholesterolemia
Treated with medicines like Lipitor,
Mevacor, Zocor
 Autosomal Codominant
 Defective Hemoglobin on
RBCs caused by 1
nucleotide base deletion
 shape change
 Damage to brain, heart,
lungs
 Carriers are protected from
malaria
 African descent; 1/10
African Americans in US is
a carrier
 Holandric Traits: genes on the y chromosome;
carry genes for male sexual characteristics
 Absence of these genes causes female
development
 Small arm of y chromosome responsible for
individuals that have a sex chromosome
combination that does not match their
appearance
XX males and XY females due to absence
or presence of SRY factor
 Ghengis Khan
Mongolian warrior 13th century
8% of men living in region that was once
Mongolian empire have same y
chromosome
 sex-linked recessive
 On 1 of 2 genes
producing clotting factor
located on the X
chromosome
 Most Common in males
 “Bleeder’s Disease”
 Bleeding spontaneously
and in joints
 Queen Victoria:
descendents affected
with hemophilia
 sex-linked recessive
 Most Common in males

1/3500
 Progressive muscle
weakening and
enlargement
 Dystrophin

Protein that provides
support for the cell;
without it, cell enlarges
and explodes
 sex-linked recessive
 On 1 of 3 color vision
genes on the X
chromosome
 Cannot distinguish
between different
colors
 Most common type is
red/green
colorblindness
 Heterozygous female
is considered a carrier
 Chromosomal
(Autosomal)
 Trisomy 21
 Mild to severe learning
disabilities, Distinct Facial
Features, Heart Defects,
low muscle tone
 Most Common Birth
Defect – 1/700 births
 Mother’s Age 30 –
1 in 1000
 Mother’s Age over 45 –
1 in 25
 Can live until 50s
 Chromosomal (Sex
chromosomes)
 Trisomy XXY male
 1 per 1,000 males (most
do not know they have an
extra X chromosome)
 Feminine Characteristics,
Sparse facial and body
hair, dental problems, tall
 Infertile (cannot produce
sperm)
 Chromosomal (Sex
Chromosome)
 Monosomy XO female
 Infertile, Short stature,
 Overweight, Some
learning difficulties,
Webbed Neck, no
menstruation
 1 out of 2,000 live births.
 96-98% do not survive to
birth
 Chromsomal
(Autosomal)
 Trisomy 18
 Elfin Appearance, Low
set ears, Clenched
hands, Heart disease,
Kidney problems, Low
birth weight, Small
head, Small jaw
(micrognathia)
 1 out of 3,000 live births
 90% die within first 6
months
 Chromsomal
(Autosomal)
 Trisomy 13
 Cleft Lip and Palate,
Polydactyly, Cleft lip or
palate, Close-set eyes
(eyes may actually fuse
together into one), Lowset ears, Severe learning
difficulties, Seizures.
Small eyes, Small head
 1 in 10,000 births
 80% die within first month
Chromosomal Disorders
Remember that meiosis is the reductional cell division that
divides one diploid cell to produce four haploid gametes (sex
cells, sperm or egg). Normally gametes have one copy of
each chromosome.
1. Sometimes chromosomes might not separate properly during
meiosis; this is called nondisjunction.
2. If nondisjunction occurs, abnormal numbers of chromosomes
(usually one is missing or there is an extra copy of one) are
found in gametes and disorders of chromosomal numbers
may result.
gametes
3.
Trisomy: Some chromosomal disorders are caused by
having three copies of one chromosome. This is
called trisomy. In trisomies, the gamete of one parent
donated two of one type of chromosome to the child
and the gamete of the other parent donated one
chromosome (like normal).
4.
Monosomy: Chromosomal disorders characterized by
missing one chromosome are called monosomies. In
monosomies, the gamete of one parent donated one
chromosome and the other did not donate any.
EXTRA!!!
NOT IN NOTES
 “Cat’s Cry” Syndrome
 Deletion of a portion
of Chromosome 5
 Developmental delay,
Moon-shaped face,
Heart disease,
Malformed larynx
 1 in 216,000 births
 Normal lifespan
Aniridia-Wilms Tumor Syndrome
#11 Deletion of upper arm
Developmental delay,
Blindness, Tumors on
kidneys
1 in 50,000,000 births
Short lifespan
Thirteen Q Deletion Syndrome
#13 Deletion of lower arm
Developmental Delay,
Malformed face, No
thumbs, Heart disease
1 in 500,000 births
Short lifespan
Triple X Syndrome
Tall stature, Mild facial
characteristics (increased width
between eyes and
proportionately smaller head
size), learning disabilities,
speech and language delays,
poor coordination, introverted,
normal sexual development
1 in 2,500 births
Normal lifespan
XYY Syndrome
XYY only; #23 Trisomy
Highly variable: sometimes
taller than average, increased
risk of learning disabilities,
delayed speech and language
skills, behavioral problems,
normal sexual development
1 in 1,000 males
 Genomic Imprinting: variation in
phenotype expression depending
on which parent gave the
chromosome



Chromosome “remembers” which
parent it came from
EX: Deletion of Chromosome 15
Prader-Willi: uncontrollable eating,
diabetes, mental retardation
Deletion of portion of paternal 15

Angleman’s: behavior problems, some
mental retardation
 Deletion of portion of maternal 15
 Presence of gene on a
sex chromosome (X or
y)
 X chromosome is larger
than y  more genes
carried on the X
 X-Linked Genes: genes
found on X chromosome



Appear mostly in males
Only one copy of X;
nothing to counteract
“bad gene”
Females would need
two copies to express
trait