Exam 2 Flashcards
what is the coeficient of relationship?
the expression of probability of sharing a common gene from an ancestor. 50% is added each generation (1/2 for siblings and 1/8 for first cousins)
what sex would be most affected from an x-linked dominant disease? how often would you see it (assuming each generation had both boys and girls)
females (since the boys all get a Y from their father)
you would see it every generation
what are the 3 rules for X chromosome inactivation?
- its random
- its fixed
- its incomplete
what is one of the few active genes in an inactivated X c’some? what does it do?
XIST - it makes a molecule (protein?) that coats the inactive X thus maintaining its inactivation
how do sex-linked genes genes (disorders) appear in males vs. females?
(sex linked is inheritance due to x-linked genes)
they will appear like autosomal recessive genes in females
it males they will appear dominant since they only have the single X
list 3 sex-linked disorders
- hemophilia A
- duchennes muscular dystrophy
- red-green color blindness
name 2 requirements for a daughter to get an x-linked recessive disorder
- is the father must be affected
2. OR it could be from a new mutation
explain how x-linked recessive disorders can “skip a generation”
if the father is affected and the mother is not then they can only have carrier children (father cant give it to son and all daughters will be affected).
if one of the carrier daughters has children with an affected male then it will manifest again
what causes hemophilia A?
a defect in factor VIII gene on chromosome X
what determines the severity of hemophilia?
the percent of normal factor VIII activity
- severe = less that 1%
- moderate = 1 to 5%
- mild = 5 to 25%
what is usually the leading cause of death in patients with duchenne muscular dystrophy?
what is an early diagnostic indicator ?
its characterized by severe, progressive muscular atrophy. cause of death is usually cardiac or respiratory failure around age 25
creatine kinase released by muscles (can be 20X normal limit)
what is the molecular cause of DMD?
a mutation in the dystrophin gene (the largest known human gene) causing the protein to usually be completely absent.
dystrophin is usually found on the cytoplasmic side of the membrane aiding in ctyoskeletal integrity bt binding F-actin and dystroglycan in the membrane
what proteins absorb color for sight?
what is deuteranopia? protanopia?
opsins
deuteranopia - no green vision
protanopia - no red vision
why is red and green vision usually lost together?
is the condition dominant or recessive?
necause they are both on the same chromosome (x) and they are very close together
also because their sequence is similar?
X-linked recessive
whats more common, x-linked recessive or dominant disorders?
do x-linked disorders affect more men or women?
dominant disorders are much more rare
they usually affect women more (because often time the disorder will be fatal in the male who only has one X)
list 3 x-linked dominant disorders and what they do
- hypophophatemic rickets - kidneys can absorb phosphate leading to abnormal ossification where bones bend and distort
- incontinentia pigmenti - abnormal skin pigmentation and teeth
- rett syndrome - causes autism, ataxia and mental retardation
what is another term for y-linked inheritance. what are these disorders usually related to?
holandric inheritance
they usually have something to do with sex determination, spermatogenesis and/or testicular function
where does mitochondrial inheritance come from? why do these genes have a high mutation rate?
they come from the mother because the egg has mitochondria in it (sperm mito doesn’t make it into zygote)
the rate is high because the mito doesn’t have any DNA repair systems for its DNA and there are a lot of free radicals from oxidative phosphorylation
list 3 mitochondrial disorders. what do these disorders do?
- leber hereditary optic neuropathy (LHON) - optic nerve death by age 30. [heteroplasmy rare. missence mutation in protein coding]
- myoclonis epilepsy with ragged red fibers (MERRF) - causes epilepsy, ataxia, dementia and myopathy. very heteroplasmic. [single base change in tRNA]
- mitochondrial encephalomyopathy and stroke-like episodes (MELAS) - self explanitory. heteroplasmic. [single base change in tRNA]
what is heteroplasmy?
the mixture of one or more organelle genomes (ex. mitochondrial DNA) which can lead to variable expression if one copy is mutated
what is the most common form of inheritable mental retardation?
fragile X syndrome. (downs is ore common but its not heritable)
what is the genetic cause for fragile x syndrome?
what are some symptoms/characteristics?
repeated CGG bases at the 5’ end og the FMR1 gene.
- individules with > 230 repetes are affected
- between 50 to 230 are carriers (transmitting males)
- less than 50 are not affected
-long faces, prominent jaw, long ears, metal retardation
what parental chromosome deletion leads to the following conditions:
- prader-willi:
- angelment:
- prader-willi: paternal deletion (maternal imprinting)
2. angelment: maternal deletion (paternal imprinting)
what is classical galactosemia? what are symptoms?
a defect in the enzyme galactose-1-phosphate uridyl transferase which prevents the conversion of galactose to glucose
- failure to thrive
- hepatic insufficiency
- cataracts (from galacticol)
- developemental delays
- in the long term, poor growth and mental retardation
what is hereditary fructose intolerance?
a defect in fructose 1,6 bisphosphate aldolase (AKA aldolase B)
affected individuals cant ingest fructose
what is von gierke disease? what are symptoms?
a defect in glucose-6-phosphase. its a glycogen storage disorder where glucose from glycogen is not released from the liver
symptoms include hepatomegaly and hypoglycemia (liver, skeletal muscle and kidneys are affected)
what is phenylketonuria?
a defect in the phenylalanine hydroxylase gene leading to an accumulation of phenylalanine.
high phenylalanine disurpts brain:
- myelination
- protein synthesis
- eventually produces retardation
what is maple syrup urine disease?
a disorder where yuo can digest branched chain amino acids (valine, leucine, isoleucine)
the accumulation of the branches chain AAs can lead to neurodegeneration and death in months
most common in mennonite communities
what is MCAD deficiency?
a deficiency in medium-chain acyl-coenzyme A dehydrogenase which leads to an accumulation of intermediate fatty acids which basically results in the inability to make ketones which the brain needs.
patients will experience episodes of hypoglycemia after fasting. fasting for too long can cause edema and exhaustion of glucose followed by death
what is congenital adrenal hyperplasia (CAH)?
a block in corticosteroid synthesis. this causes a buildup of the precursors which are usually androgens or converted to weak androgens. the result is a mascinulization of females in utero.
severe forms can result in salt-wasting (large amount of renal salt excretion when the body needs it) which leads to weight loss, lethargy, dehydration and death
what is zellwegger syndrome?
a mutation in the proteins needed for peroxisome biogenesis.
symptoms are neonatal hypotonia, progressive white matter disease, distinctive face and death in infancy
what are mucopolysaccharidoses?
a lysosomal storage disorder characterized by a reduced degradation of glycosaminoglycans (hepran, dermatan, keratan and condroitin [all sulfates])
there are 10 enzymes than cause 6 disorders
what is sphingolipidoses? list 3 specific disorders and what causes them.
anyother type of lysosomal storage disease where shpingolipid degeneration is deficient
- gaucher disease: beta-glucosidase deficiency (ashkanazi jews, cherry red macula)
- tay-sachs: beta-hexosamididase
- niemann-pick: sphingomyelinase deficiency
what is I-cell disease?
the phosphotransferase that attaches mannose-6-phosphate to proteins (which is used to target it to the lysosome) is deficient leading to the formation of lysosomes that cant digest anything. they become inclusion bodies
what are the 4 urea cycle disorders? what are the common symptoms of them all?
they are caused by defects that cause accumulation of precursors
- carbamoyl phosphate synthetase (CPS)
- ornithine transcarbamoylase (OTC) [most common, x-linked]
- argininosuccinate synthetase (ASA)
- argininosuccinase (AS)
lethargy and coma. depending on the deficiency, the buildup will be different but it ultimately all leads up to buildup of toxic ammonia
what is cystine?
two cysteins with a disulfide bond
what is cystinuria? dominant or recessive?
a defect in transported for dibasic amino acids (cystern) which prevents its excretion.
the buildup of cystein can lead to the formation of kidney stones
its autosomal recessive (and common)
what is wilson disease?
a defect in copper excretion (ATP7B gene) to the biliary tract causing accumulation of Cu in the liver (also accumulates in the eye and joints)
causes:
- Kayser-fleischer ring in the eye (a dark pigment around the outside of the iris)
- acute or chronic liver disease
- dysarthria (poor speech)
- diminished coordination
- arthropathy (joint disease)
- cardiomyopathy
- kidney damage
- hypoparathyroidism
what is hereditary hemochromatosis? how do yuo diagnose it?
a condition characterized by an excessive iron absorption in the intestines
you take a liver biopsy and look for hemosiderin accumulation
what is a centimorgan?
one centimorgan is a 1% chance of recombination between two genes. therefore the less cMs the more likely the genes will not undergo independent assortment from each other
what is a LOD score used for? what values are significant?
calculating the likelihood that two genes are linked or not
- value >3 is significant for linkage
- value <-2 suggests no linkage