Download Genetic Diseases

Genetic Diseases
Caused by errors in genes that are
passed from parents to offspring.
Types of Genetic Disorders

Chromosome Disorders – parts of or entire
chromosomes are missing OR there are
extra copies
– Common cause is nondisjunction – failure of
homologous chromosomes to separate during
meiosis


Chromosomal Disorders can be seen on a
karyotype.
A Karyotype is a picture of the
chromosomes arranged in pairs in order of
decreasing size.
– A normal person has 46 chromosomes
• 44 are autosomes & the last two are the sex
chromosomes
Trisomy 21
(Down’s Syndrome)



Have 3 copies of chromosome
#21 (chromosome disorder)
shorter; heart and intestinal
defects; poor muscle tone;
learns to walk and talk later
Before age 35 1/760 chance and after
age 35 there is a 1/77 chance of
having a down’s baby.
EOCT Practice Question:





A karyotype of a person with
Down syndrome is shown
here. Which term is used to
describe this type of genetic
disorder?
A) deletion
B) recombination
C) transformation
D) trisomy
Klinefelter’s Syndrome





male XXY; most are sterile
have underdeveloped male secondary sex
characteristics.
This is relatively common (about 1 in 500 males).
Affected males are usually normal, though they may be tall and
have small testes.
Infertility results from
absent sperm.
Turner’s Syndrome


Female XO; sterile
poorly developed reproductive organs.
affects about 1 in every 2,000 female births and 10% of
miscarriages.
 TS is characterized
clinically by short stature,
ovarian failure, and a
variety of other features
such as extra neck skin

Eoct Practice Question





The karyotype represents a
meiotic accident called
__________ which, in this case,
results in a condition called
____________. This condition
causes females to be short in
stature, lack secondary sex
characteristics, and to be sterile.
A)deletion; metafemale
B)deletion; Klinefelter
syndrome
C)nondisjunction; Down's
syndrome
D)nondisjunction; Turner's
syndrome
Types of Genetic Disorders

Autosomal Dominant Disorders –
controlled by a dominant allele on a non-sex
chromosome

Autosomal Recessive Disorders -controlled by a recessive allele on a non-sex
chromosome
Phenylketonuria (PKU)



Can’t change phenylalanine
into tyrosine. The build up of
phenylalanine poisons brain
cells.
Treated by diet; treatment
prevents damage but does not
cure disease
Autosomal Recessive
Disorder
Cystic Fibrosis



Autosomal Recessive
Disorder
Most common in those of
Northern European descent
abnormal amounts of mucus
are produced in the
respiratory tract; mucus clogs
breathing apparatus
Tay Sachs Disease





Autosomal Recessive
Disorder
Cannot produce a blood
enzyme needed to break
down fats
fats accumulate in cells, cells
rupture and die
results in blindness, deafness,
mental degeneration, death.
Occurs most frequently in
those of Jewish descent
Sickle Cell Disease


abnormal hemoglobin molecules in red blood
cells cannot carry O2 effectively; sickled
shape cells cannot travel through small blood
vessels (autosomal recessive disorder)
Most common in African Americans
homozygous
recessive= sickle cell
disease
heterozygous= sickle
cell trait; defense
against malaria
(codominant)
Polydactyly


Autosomal Dominant Disorder
Having extra fingers or toes
Huntington’s Disease



Autosomal Dominant Disorder
Symptoms do not occur until after age 30
(may have already unknowingly passed the
gene to your children)
Progressive nervous system deterioration
until death occurs
Types of Genetic Disorders

Sex-linked Disorders – controlled by alleles
on the X chromosome
– Sex-linked recessive traits are expressed more
often in males because they only have one X
chromosome
Color Blindness


Sex-linked trait
Inability to distinguish
between certain colors (redgreen colorblindness is most
common)
Hemophilia



Sex-linked trait
Blood lacks the protein necessary for
normal blood clotting
Treated by injections of normal clotting
proteins