albinism an angelman quiz Flashcards
Angelman syndrome defined by
mental impairment, excessively happy demeanor, jerky movements, sleep disturbance
what jerky movements in angelman are common
hand flapping
how many ppl are affected by angelman
1 in 20,000 live births
does Angelman SYndrome present the same phenotype in its patients
yes
the multiple mechanisms for angelman phenotype
imprinting and deletion
imprinting errors
uniparental disomy
genetic imprinting
when one copy of a gene is “turned off” after it is inherited
genetic imprinting is usually caused by
methylation
methylation
additon of methyl group -CH3 o a gene
the methyl group in genetic imprinting does what
blocks transcription from happening> DNA never becomes RNA>never makes protein
(imprinting) for many genes, either the mother’s chromosome or the father’s chromosome is
systematically silenced
what is a gene always silenced in sperm, not in eggs
UBE3A
where is UBE3A located on
on the 15th chromosome
UBE3A codes for
protein E6-AP
E6-AP is involved in what
the ubiquitination process
what is ubiquitination process
cell’s way of targeting and destroying certain proteins
since the father’s copy of UBE3A is always silenced,
the mother’s copy becomes extremely important
in about 75% of cases of Angelman
a chromosomal deletion mutation leads to the complete deletion of this gene in the egg
if there is a deletion of UBE3A in the egg
since the father’s copy is silenced the baby will have no functioning copies of E6-AP
UBE3A gene is located very close to
P gene (causes type 2 albinism)
since UBE3A is so close to P gene
chromosomal deletion mutation will affect both genes» albinism more common in people with Angeman
what percentage of Angelman is an imprinting error
20%
what is the imprinting error that causes Angelman
the mother’s copy of the gene is methylated w/ the fathers
result of imprinting error
both copies are off, phenotypes look the same as if mom’s gene is missing
rare cases of Angelman syndrome
cause by uniparental disomy
uniparental disomy is
rare condition where . zygote inherits two copies of a chromosome from one parent and no copies from another
two forms of uniparental disomy
uniparental isodisomy
uniparental heterodisomy
uniparental isodisomy
when a person inherits the SAME chromosome from a parent twice
what cases would uniparental isodisomy happen
where a person would have a monosomy but undergoes a monosomy rescue
what is a monosomy rescue
the single chromosome is duplicated
a person who underwent a monosomy rescue will have
46 chromosomes, but 2 identical copies of the same one
uniparental heterodisomy occurs when
there would be a trisomy but the zygote undergoes trisomy rescue
trisomy rescue
one copy of the tripled chromosome discarded
in how many cases of trisomy rescue will the embryo be normal
2/3
in _____ cases of trisomy rescue___
1/3 cases, the embryo could inherit two copies of one parent’s chromosomes
uniparental disomy can be the cause of AS when
-a person inherits 2 copies of father’s 15th chromosme, none from mom
when 2 copies of father’s 15th chromosome inherited
both copies of father’s UBE3A gene silenced by methylation,»_space;> AS phenotype
AS rember
3 unique genotypes lead to same phenotype
albinism
lack of pigment melanin
two main types of albinism
- oculocutaneous albinism
- ocular albinism
oculocutaneous albinism
affects skin, hair , eyes
ocular albinism
eyes only
people w/ oculocutaneous albinism have ..
extremely fair skin, white-blonde hair, light blue eyes
melanocytes do what
produce black pigment melanin that makes skin look dark
melanocytes produce more melanin in response to
more sunlight exposure
melanocytes package small amounts of melanin into
vessels called melanosomes
melanosomes are passed on tp
superficial keratinocytes
what does melanin do
absorbs UV rays from sun that can give u cancer
skin color is determined by what
fatctor of number f melanosomes, how active melanocytes are
what does NOT determine skin color
Aiyana
A melanocyte generally ha
ling projections called dendrite that reach to more superficial layers
dendrites of melancyte,…
passes melanosomes into outer cells
albinism often causes
red eyes, ,
albinism red eyes…
because w/ a total lack of pigment blood vessels in your can be seen, sensitive too sun
what type of disorder is albinism
recessive
most common mutation for oculocutaneous albinism comes in on
c
TYR gene codes
enzyme tyrosinase
two types type 1 of albinism
Type 1A: Amorphic mutation in TYR
Type 1B: Hypomorphic mutation in TYR
types of type 1 of albinism look
same at birth, gradually type 1b is more dirty blonde``
tyrosinase is
an enzyme that catalyzes an important step in the synthesis of melanin from tyrosine
without tyrosinase
melanin’s precursor can’t be mDE, MELNIN CAN’T BE MADE EITHER
melanin’s precursor
dopaquinone
type 2 oculocutaneous albinism
comes from a deficiency in a transport protein found in the membrane of melanocytes
the transport protein in the membrane of melanocytes
allows other proteins like tyrosinase to pass into the melanocyte from other cells, causing more melanin to be prduced inside
gene for the transport protein in membrane of melanocyte
P gene, found on 15th chromosme
the other types of albinism come from
mutations in other enzymes in the melanin synthesis pathway , not as common
the other types of albinism can also come from
issues w transportation in melanocytes, storing melanin correctly etc
ho many different genotypes of albinism have been seen
17+
