Transcript Human Genetic Disorders

Key Concepts
•What
are two major causes of genetic
disorders in humans?
•How
traits?
•How
do geneticists trace the inheritance of
are genetic disorders diagnosed and
treated?
Key Terms
Genetic disorder
 Karyotype
 pedigree

Causes of Genetic Disorders
Genetic disorder – abnormal condition
that a person inherits through genes or
chromosomes
 Some are caused by mutations in the
DNA of genes
 Others are caused by changes in the
overall structure or number of
chromosomes

What Can Go Wrong?

Nondisjunction (most deadly)
 Improper
separation of homologous
chromosomes in meiosis I or chromatids in
mieosis II or mitosis (at an early embryonic
stage)
 Results in too many or too few chromosomes
in daughter cells

DNA mutations
 More
specific letter-changes in code
 Results in the inability to make certain proteins
Cystic Fibrosis
Body produces abnormally thick mucus
in the lungs and intestines
 The thick mucus fills the lungs making
it hard to breathe
 Caused by recessive
 allele on one chromosome
that is the result of a
mutation in which 3 base
pairs are removed from a
DNA molecule

Sickle- Cell Disease
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Affects hemoglobin, protein in
blood that carries O2
When o2 concentrations are low
blood cells have a sickle shape
The sickle shape can clog blood
vessels and cannot carry as much
O2 as normal shaped red blood
cells
The allele is codominant with
normal allele
A person with 2 sickle shaped
alleles will have the disease
One allele and the person will
produce both normal and sickle
shaped cells. These people will
not usually have symptoms of
the disease
Hemophilia
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A person’s blood clots
very slowly or not at all
Do not produce one of the proteins needed
for normal blood clotting
Small bumps and bruises may cause
internal bleeding that can’t be controlled
Caused by a recessive allele on the X
chromosome
Sex-linked disorder – occurs more
frequently in males
Nondisjunction Causes:

Aneuploidy: cells that have too many or
too few chromosomes are aneuploid.
 Monosomy:
only 1 of a pair present
 Trisomy: 3 instead of 2 present
Down Syndrome
Trisomy 21

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
Have an extra copy of
chromosome 21 (instead of
a pair the person has 3 copies)
Most often occurs when
chromosomes fail to separate
properly during meiosis
Have some degree of Intellectual
and Developmental Disabilities.
Heart defects are also common,
but can be treated
Down Syndrome
Caused by Trisomy 21
 Symptoms:

 Intellectual
and Developmental
Disabilities
 Flattened
face
 Sparse, straight hair
 Short stature
 High risk of cardiac anomalies, leukemia,
cataracts, and digestive blockages
 Average life expectancy: 55 years (much
longer than it used to be even just recently)
Karyotypes
Picture of all the chromosomes in a cell
 Arranged in pairs
 Can reveal whether a person has the
correct number of chromosomes

Pedigrees
Chart used to trace
the inheritance of
traits in humans
 Can track ordinary
traits or a genetic
disorder

Family Pedigrees
Family Pedigrees
Managing Genetic Disorders
Doctors used to only have Punnett
Squares and pedigrees to help predict
genetic disorders
 Now they have tools such as karyotypes
to help diagnose genetic disorders
 People with genetic disorders can be
helped through medical care, education,
job training, and other methods

Genetic Testing

Amniocentesis and Chronic Villi Sampling
 Sample

of amniotic fluid or placenta
Karyotyping
 Taking
a picture of the chromosomes in a cell
Genetic Counseling
A couple with a family history of a
genetic disorder can go to a genetic
counselor for advice
 Help couples understand their chances
of having a child with a
particular genetic disorder

Dealing with Genetic
Disorders
Medical treatments help people with some
disorders
 Ex. Physical therapy helps remove mucus
from the lungs of people with cystic
fibrosis
 Taking Folic Acid helps people with sicklecell disease make more red blood cells
 Education and job training helps people
with Down Syndrome find work in a
variety of places of employment

Incidence of Genetic Abnormalities

Maternal Age
 At
25 years, 17% of eggs may have
chromosomal abnormalities. At 40 years, up
to 74% may contain abnormalities.

Spontaneous Abortion (Miscarriage)
 Two-thirds
of all pregnancies are lost. These
miscarriages are called spontaneous
abortions.
 Genetic mutation causes an estimated 60% of
these spontaneous abortions.
Sex Chromosome Abnormalities

Turners Syndrome (X0 - female)
1
in 2000
 Infertile, sexually underdeveloped, short
stature, narrow aorta, normal intelligence

Klinefelter Syndrome (XXY - male)
1
in 1000
 Reduced sexual maturity, secondary sexual
characteristics (breast swelling), no sperm
production
Sex Chromosome Abnormalities

Triple X Syndrome (XXX – female)
1
in 1500
 Slight IQ reduction, menstrual irregularities

Jacob Syndrome (XYY – male)
 Incidence
unknown (lack of diagnosis)
 Tall, acne issues, speech/reading problems
 Disproportionate number incarcerated
 96% are normal (most don’t realize they have
this condition)
DNA Mutations

Cri du Chat Syndrome (cry of the cat)
 Deletion

on part of chromosome 5
Fragile X
 Repeated
sequences of CCG on X
chromosome
 Normal = 6-50 copies
 Carrier (males) = 50-230 copies
 Disorder = more than 230 copies
 Causes mental retardation (2nd behind only
Down Syndrome)
Autosomal Recessive Disorders

Cystic Fibrosis (CF)
 Mutation
on chromosome 7
 Thick mucous develops in lungs and digestive
tract
 Difficulty breathing & lung infections
 Most common lethal genetic disorder
 1 in 25 is a carrier
 1 in 2500 has disorder
More Autosomal Recessive

Tay Sachs Disease
 Fatty
substance builds up in neurons
 Gradual paralysis and loss of nervous function
by age 4-5
 Single defective enzyme
 Heterozygote carriers (Hh) do not have
disorder, but are resistant to Tuberculosis
 Especially common in Jewish population
(central and eastern European descent), up to
11% are carriers
More Autosomal Recessive

PKU (Phenylketonuria)
 Can’t
break down amino acid phenylalanine
(missing critical enzyme)
 Phenylalanine builds up and interferes with
nervous system leading to mental retardation
and even death
 Early screening  phenylalanine restricted
diet for children with disorder
More Autosomal Recessive

Sickle-Cell Anemia
 Abnormality
in hemoglobin (carries oxygen in
our red blood cells)
 Cells become sickle-shaped and clog blood
vessels (painful)
 Causes poor circulation, jaundice, anemia,
and hemorrhaging
 Heterozygote carriers (Hh) do not have
disorder and are resistant to malaria
 8-10% of Africans (or descendants) are
carriers
Sickle-Cell Anemia Photo
Autosomal Dominant Disorders

Neurofibromatosis (NF)
 Could
be “Elephant Man’s” disorder
 As mild as tan spots on skin
 Could cause severe deformities, tumors, even
death
 1 in 3000 newborns
 Mutation on chromosome 17
Autosomal Dominant Disorders

Huntington’s Disease
 Brain
cells degenerate, causing involuntary
muscle jerks, slurred speach, loss of balance,
mood swings, memory loss, incapacitation
 Progressive: eventually causes death
 Onset: 35-45 years old
 Repeated sequences of AGC on chromosome 4
 Diagnostic test available, but no cure
 Would you want to know?
X-Linked or Sex-Linked Traits
Traits located on X Chromosome
 Males have them more often than females

 They
only have one X chromosome
X-Linked or Sex-Linked Traits

Colorblindness (3 types – Red/Green most
common)
X-Linked or Sex-Linked Traits

Hemophilia
1
in 1500 males
 Lack a blood clotting factor
 Can bleed to death from wounds or bruises
(internal bleeding)

Duchenne Muscular Dystrophy
1
in 5000 males
 Muscular deterioration starts 3-5 years old
 Wheelchair by 12, rarely survive past 20