Transcript Human Genetics - Esperanza High School

Human Genetics
Human Genetic Disorders
• Genetic abnormality = a genetic
condition that is a deviation from
the average: not life-threatening
• Genetic disorder = describes
conditions that
cause medical
problems
Karyotype
• A pictorial display of metaphase
chromosomes from a mitotic cell
• Chromosomes are identified and arranged
by their
characteristic
size, shape,
centromere
location and
staining patterns
Human Karyotype
Amniocentesis
Detects some
fetal
abnormalities
through
karyotyping
Human Chromosome
Characteristics
• Diploid set for humans = 46
• Autosomes = 22
• Female-sex chromosomes =
homologous (XX)
• Male-sex chromosomes =
non-homologous (XY)
Autosomal Recessive
• Either parent
can carry the
recessive allele
on an autosome.
– Heterozygotes
are symptomfree.
– Homozygotes
are affected.
Genetic Errors of Metabolism
• One defective or absent
gene can result in the
inability to make a
specific enzyme
• Recombinant DNA
techniques may someday
correct faulty
chromosomes
Obesity gene discovered
Genetic Errors of Metabolism
• Galactosemia
–Inability to metabolize lactose
• Cystic Fibrosis
–Inability to
breakdown
mucous in lungs
and other organs
Tay-Sachs Disease
• Missing an enzyme
to break down lipids,
leading to destruction
of central nervous sys.
• Mainly found in Eastern European
Jewish decendents 1:27 is a carrier
– Judaism is trying to eliminate gene
through non-breeding between couples
who are carriers
Sickle-cell Anemia
• Recessive, changes the shape of
the hemoglobin molecule
– Extremely painful, debilitating
– Only distorts when
deoxygenated
Sickle-cell Anemia
• High frequency in black populations
• SS= no sickle-cell
• Ss = mild symptom
• ss = full blown disease
Heterozygote Superiority
• Heterozygotes receive protection from
symptoms of sickle-cell AND malaria advantage in malarial countries
• SS + malaria =
malaria only
• Ss + malaria =
no symptoms of either
• ss + malaria =
mild sickle cell
Complications
• Sickle cells become trapped and
destroyed in the spleen causing
Splenic Sequestion
• Anemia
• Pain episodes
• Stroke or Brain Damage
• Kidney failure
• Pneumonia
• Increased Infections
PKU
• Lack one enzyme to break
down phenylalanine
– Products
accumulate, cause
mental retardation,
other severe
symptoms
– Treated through
dietary restrictions
Autosomal Dominant
• A dominant allele is always
expressed and if it reduces the
chance of surviving or
reproducing, its frequency should
decrease
• Mutations and conditions that set
in late in life work against this
Autosomal Dominant
• Achondroplasia (Dwarfism)
–Lacks functional gene for somatropic
hormone in the pituitary
Errors in Metabolism
• Acromegaly (Gigantism)
– Pituitary produces
excess growth
hormones
Huntington’s Disorder
• A serious degeneration of the
nervous system with an onset from
age 40 onward - Fatal, no cure
Would
you want
to know?
• Gene has
been
found
WHY???
Woody Guthrie
X-Linked Recessive
• Mutated gene
occurs only on
the X
chromosome
X-Linked Recessive
• Heterozygous females are
phenotypically normal
• Males are affected because
they have only one
allele for the trait (on the
X chromosome) and it
can be recessive.
X-Linked Recessive
• Color-blindness
• Baldness
Hemophilia A
• Inability of blood to clot because genes
do not code for clotting agent(s)
Queen Victoria: a Carrier
Hemophilia A
• Afflicted persons need frequent
transfusions and infusions of artificial
clotting agents
• Internal bleeding from falls or bruising
the most serious
• Cummulative scarring may
restrict movement
X-Linked Dominance
• Similar to X-linked recessive alleles,
except the allele is also expressed in
heterozygous females
• Examples: faulty
enamel (of the teeth) trait
Patterns of Inheritance
• Aneuploidy = one extra or one less
chromosome, may affect one of every
two newly fertilized eggs
• Polyploidy = three or more of each
chromosome, is common in plants but
is lethal to the zygote if it occurs in
humans
Meiotic Errors
• Nondisjunction- homologues don't
separate in meiosis 1
Nondisjunction
in Sex
Chromosomes
• Homologues
don't
separate in
meiosis 1
Trisomy 21/Down Syndrome
• Occurs more frequently
in children born to
older women and men
– 1 in 80 births after 40 yrs
– 1in 40 births after 45 yrs
Down Syndrome
• Most children show mental deficiencies
– Many lead productive lives
– 40% have heart defects
– many have diabetes and
have weight issues
Turner Syndrome
• XO
– Females with only one X chromosome,
mostly due to nondisjunction in father
– Most are spontaneously aborted
– Sterile, short stature,
heart defects, premature
aging, shorter lives
• YO = LETHAL
Klinefelter Syndrome
• XXY condition
– Most from non-disjunction in mother
– Tall, some mental slowness
– Poor male sex organ development;
breast development;
usually sterile
Jacob Syndrome
• XYY condition
• Fertile, tall, slight retardation,
increased strength & aggression
• NOT predisposed to crime - a fallacy
Changes in
Chromosome Structure
• Translocation
– Transfer of
a piece of
one
chromosome
to another
Changes in
Chromosome Structure
• Deletions
– Loss of a
chromosome region
by viral attack,
chemicals,
irradiation, or
other environmental
factors
Cri-du-Chat
• Deletion or translocation of
material from 5th chromosome
–“Cry of the Cat” (French) - sound
many children make
when crying
– Severe mental
retardation; internal
problems
Changes in
Chromosome Structure
• Inversion
– Alters the position and sequence of
the genes so that gene order is
reversed
Changes in
Chromosome Structure
• Duplications
– Occurs when a gene
sequence is in
excess of the normal
amount.
Duplications
• Fragile X syndrome
– Mental retardation
– Repeats that may block
expression of gene on
X chromosome
Mistake Summary
Designed
by
Anne F. Maben
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