Transcript human genetics - local.brookings.k12.sd.us

HUMAN GENETICS
What can go wrong?
Chromosome
Mutations
Gene
Mutations
Chromosomal Abnormalities
• 1 infant in 200 newborns has a
chromosomal abnormality
• 28% of first trimester miscarriages have
a chromosomal abnormality
• Abnormalities in larger
chromosomes don’t usually survive
A change in the DNA code of an
organism is called a
______________________
MUTATION
Mutations can be
HARMFUL
BENEFICIAL OR ______________
_______________
BENEFICIAL MUTATIONS
Help an organism survive
and reproduce
Provide variation in population for
natural selection to act upon
Image from:
http://www.cheryllavender.com/Snow%20Rabbit.jpg
HARMFUL MUTATIONS
Can result in death =___________
LETHAL
(even before birth)
Cause a genetic disorder
Cause cancer
SOMATIC CELL MUTATIONS
If the change happens in a BODY CELL
(lung, liver, brain, muscle, etc.)
= ______________________
Somatic cell mutation
Somatic cell mutations can:
Cause cancer
______________________
Make
cell not able to function
______________________
Kill cell
_____________
BUT won’t be passed on to offspring
GERM CELL MUTATION
If the change happens in Gametes
(sperm & eggs)
= _______________________
Germ cell mutation
 Can be passed on to offspring
HUMAN GENETICS
What can go wrong?
Chromosome
Mutations
Gene
Mutations
Changes in chromosome number
Missing
chromosomes (monosomy)
____________________________
EX: Turner’s syndrome - X0
Extra
chromosomes
(trisomy)
____________________________
EX: Down’s syndrome – 3 #21’s
Kleinfelter’s syndrome- XXy
NON-DISJUNCTION
A homologous pair sticks together and
doesn’t separate at MEIOSIS.
One cell gets 2 copies of
the chromosome the
other cell gets none.
Normal Meiosis
Nondisjunction
Nondisjunction
• Chromosomes don’t
separate at anaphase
• Cell gets 2 copies of a
chromosome OR none
• After fertilization new
baby gets 3 of each
chromosome (trisomy)
or only 1 copy of each
(monosomy)
Normal division
Non-disjunction
Human Abnormalities
Caused by Non-Disjunction
Down’s syndrome
Patau syndrome
Kleinfelter syndrome
Turner’s syndrome
Xyy
Turner’s syndrome
(monosomy)
Turner’s syndrome XO
•
•
•
•
•
•
•
•
1 in 5000 births
Female = XO
Small size
Slightly decreased intelligence
35% have heart abnormalities
Hearing loss common
Broad chest
Undeveloped ovaries/can’t have children
Kleinfelter syndrome Xxy
(trisomy)
Kleinfelter syndrome
• 1 in 1000 births
• Male = XXy
• Average to slight decrease in
intelligence
• Small testes/
can’t have children
• Usually not discovered until
puberty when don’t mature
like peers
Xyy syndrome
• Xyy males
• Taller
• Average
intelligence
• Some study
show increased
learning
disabilities
• Lead normal
lives
Down’s syndrome (trisomy 21)
Down’s syndrome (trisomy 21)
• 1 in 660 births
• Similar facial
features
• Slanted eyes
• Protruding tongue
Down’s syndrome (trisomy 21)
Simian line on palm
Down’s syndrome (trisomy 21)
• Most common
chromosomal
abnormality
• 50% have heart
defects that need
surgery to repair
• Mental retardation
• Risk increases with age
of mom
Patau syndrome (trisomy 13)
Patau syndrome (trisomy 13)
• Can be traced back 300
years in literature
• 1st identified as a
chromosomal cause in
1960
• 1 in 7000 births (rare)
Patau syndrome (trisomy 13)
Cleft lip & palate
Eye abnormalities
(too small or
missing)
Patau syndrome (trisomy 13)
Low set ears
Polydactyly
HUMAN GENETICS
What can go wrong?
Chromosome
Mutations
Gene
Mutations
DELETION
________________________________________
Piece
of whole chromosome is lost
Image from:
http://www.biology-online.org/2/8_mutations.htm
Human Abnormalities
Caused by Deletions
• Wolf-Hirschhorn syndrome
• Cri-du-chat syndrome
• Prader-Willi Syndrome
Wolf-Hirschhorn syndrome (4p-)
• Missing piece on
short arm of
chromosome 4
• Mental
retardation
• Large low set ears
• Club feet
Cri-du-chat (Cat cry) (5p-)
• 1 in 50,000 births
• More common in girls
• Mewing cry in infancy
• Missing piece of number 5
• Mental retardation
• 50% have heart defects
Prader-Willi Syndrome
• Deletion in chromosome 15
• Feeding problems: poor weight gain in
infancy, won’t eat
• Ages 1-6 excessive, rapid weight gain
• Under developed sex organs
• Mild to moderate retardation
• Obsession with food
• Complications from problems associated
with obesity
(heart attack, high blood pressure, diabetes)
Prader-Willi syndrome
Victor at age 1
Victor at age 2
INVERSION
Segment flips and reads backwards
Image from:
http://www.biology-online.org/2/8_mutations.htm
TRANSLOCATION
Segment breaks off and joins a
different non-homologous
chromosome
Image from:
http://www.biology-online.org/2/8_mutations.htm
A gene that is flipped and
reads backwards
will not work.
A gene that is moved to
another chromosome
will not separate from
its partner during meiosis.
One cell can get 2 copies
of gene, one cell gets none.
HUMAN GENETICS
What can go wrong?
Chromosome
Mutations
Gene
Mutations
GENE MUTATIONS
Changes in the DNA code of a single gene
 PROTEIN
DNA  RNA
____________
______________________
___________
Harmful Gene Mutations
1. Point mutations –
changes a _________
SINGLE base in DNA code
1. __________________
Substitution
2. Frame shift mutations
changes _____________
MULTIPLE bases in code
Deletion
1. ___________________
2. ________________
Addition
SUBSTITUTION
Changes one base for another
ATT C GAG C T
ATT C TAG C T
SICKLE CELL ANEMIA
CAUSE:
(autosomal recessive)
A changed to T
(glu to val)
gene on chromosome #11
that codes for part of
hemoglobin protein
(carries oxygen in blood)
SICKLE CELL ANEMIA
SYMPTOMS:
Sickle shaped
Red Blood Cells
in hh persons
Circulatory problems
Loss of blood cells (anemia)
Organ damage
DEATH
SICKLE CELL ANEMIA
More common in African Americans
1 in 500 = hh
1 in 10 = Hh carriers for gene
Hh persons have Sickle cell TRAIT
make some normal RBC’s’ ; some
sickled cells
FRAME SHIFT MUTATIONS
Changes multiple bases in code
thefatcatranandran
the
fat cat ran and ran
____________________
DELETION
theatcatranandran
the atc atr ana ndr an
_____________________
FRAME SHIFT MUTATIONS
at beginning of gene are more
damaging than those at end because
more of gene is changed
thefatcatranandran
____________________
the fat cat ran and ran
DELETION near front
theatcatranandran
the atc atr ana ndr an
_____________________
DELETION near end
thefatcatranandrn
_____________________
DELETION
________________________________________
Piece of
DNA code for one gene is lost
Image from:
http://www.biology-online.org/2/8_mutations.htm
Duchenne Muscular Dystrophy
CAUSE:
(X linked recessive)
DELETION in
gene that codes
for a muscle
protein
Duchenne Muscular Dystrophy
(DMD)
SYMPTOMS:
1 in 3500 male births
Appears before age 5
Progressive muscle weakening
Most in wheelchair by age 13
Eventually lethal
DUPLICATION
Piece
of DNA is copied too many times
________________________________________________
Image from:
http://www.biology-online.org/2/8_mutations.htm
FRAME SHIFT MUTATIONS
Changes multiple bases in code
thefatcatranandran
the
fat cat ran and ran
____________________
DUPLICATION
thefatcatranandandandandran
the fat cat ran and and and ran
___________________________
HUNTINGTON’S
CAUSE:
Autosomal dominant
40-100 CAG Repeats
at end of gene on
chromosome 4
HUNTINGTON’S
SYMPTOMS:
Seen in both
males and females
• Degenerative brain disorder
• Symptoms appear
age 30-40
(Usually after having children)
• Lose ability to walk, think,
talk, reason
• 50/50 chance of passing it to
child
Until now people didn’t
know they had the gene,
until after they had
already had children.
Now there is a test to tell if
you have the gene before
symptoms appear.
Would you want to know
if there is NO cure?
OTHER GENETIC DISEASES
AUTOSOMAL RECESSIVE
• Phenylketonuria
• Cystic fibrosis
• Albinism
X-LINKED RECESSIVE
• Color blindness
• Hemophilia
• Muscular dystrophy
AUTOSOMAL DOMINANT
• Achondroplasia (Dwarfism)
• Huntington’s
HEMOPHILIA
CAUSE:
change in gene on X chromosome that codes
for blood clotting protein
SYMPTOMS:
More common in males
Internal and external bleeding
Can result in death
transfusions/hospitalization
required frequently to stop
bleeding
ACHONDROPLASIA
(Dwarfism)
CAUSE: (Autosomal Dominant on chromosome 4)
Most are new mutations in egg or sperm cell, but it can be
inherited from parent with gene
1 in 20,000 births
200,000 “little people” worldwide
One of oldest known
– seen in Egyptian art
Normal size torso;
short arms and legs
Problem with way cartilage
changes to bone as bones grow
COLOR
BLINDNESS
CAUSE:
X linked recessive
Mutation in gene on
X chromosome
SYMPTOMS:
More common in males
(8% of males are colorblind)
Can’t distinguish certain colors
Most common = red/green
Cystic Fibrosis
Mutation in gene on chromosome 7 that
codes for protein in membrane that
transports chloride ions
Cystic Fibrosis
Autosomal recessive
Symptoms:
More common in Caucasians
Make extra thick mucous in lungs and
pancreas which leads to respiratory and
digestive complications
Salty skin is clue
Phenylketonuria (PKU)
CAUSE:
Mutation in gene for enzyme that changes
the amino acid phenylalanine into tyrosine
Build up causes brain damage
ALL babies have blood test for PKU when born
before leaving hospital
Treatment:
Diet low in phenylalanine can extend life and
prevent retardation
* Nutri-sweet warning
All “SUGAR-FREE” foods
have a warning label
* PHENYLKETONURICS:
Contains phenylalanine
Image from:
http://www.themagicgadget.co.uk/xcart/search.php?mode=search