Glossary of USMLE Genetics

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implantation of blastocyst occurs within how long?
one week
within what week does the bilaminar disk form?
week 2
gastrulation, primitive streak, and neural plate begin to form within what week of gestation?
week 4
the embryo is extremely susceptible to teratogens during what span of weeks?
weeks 3-8
the neural tube is formed and organogenesis occurs during what weeks?
weeks 3-8
when does the heart begin to beat and the upper and lower limb buds begin to form?
week 4
by when do genitalia have male/female characteristics?
week 10
name the 2 germ layers present in week 2
epiblast, hypoblast
what 2 cavities are present in week 2?
amniotic cavity, yolk sac
what 2 components of the placenta are present during week 2?
cytotrophoblast, syncytiotrophoblast
what 3 germ layers are present in the third week and what stage is the embryo in?
ectoderm, mesoderm, endoderm; gastrula
the lens of the eye is derived from what germ layer?
surface ectoderm
what germ layer is the adenohypophysis derived from?
surface ectoderm
what germ layer is the neurohypophysis derived from?
neuroectoderm (remember 'neuro')
CNS neurons, oligodendrocytes, astrocytes are derived from which germ layer?
what are the ANS, DRG, cranial nerves derived from?
neural crest
melanocytes and parafollicular (C) cells are derived from what?
neural crest (C cells = Crest)
dura mater, CT, bone, muscle, are all derived from what germ layer?
pia, arachnoid, and Schwann cells arise from what?
neural crest
lymph, blood, spleen, kidneys arise from what?
extraocular muscles are derived from what layer?
the dermis is derived from what layer?
lungs, liver, pancreas, thymus, parathyroid all arise from what?
endoderm - gut tube epithelium and derivatives
thyroid follicular cells arise from what layer?
what is the postnatal derivative of the notochord?
nucleus polposus of the intervertebral disk
what is the role of the notochord?
induces ectoderm to form neuroectoderm (neural plate)
which is teratogenic: warfarin or heparin?
warfarin - causes multiple anomalies
exposure to ACE inhibitors in utero can have what effect on fetus?
renal damage
what is the role of the umbilical arteries?
return DEoxygenated blood from fetal internal iliac arteries
what is the role of the allantoic duct?
removes nitrogenous waste (from fetal bladder, like a urethra)
what does the truncus arteriosus give rise to?
ascending aorta and pulmonary trunk
the smooth parts of left and right ventricle arise from what embryonic structure?
bulbous cordis
the trabeculated parts of the ventricles and atria arise from what?
primitive ventricle and atria
from what embryologic structure does the coronary sinus originate?
left horn of sinus venosus
the smooth part of the right atrium comes from what?
right horn of sinus venosus
what does the SVC arise from?
right commmon cardinal vein and right anterior cardinal vein
oxygenated blood reaching the heart via the IVC is diverted through ________ and pumped out the aorta to the head
foramen ovale
this structure provides a pulmonary-to-systemic shunt
ductus arteriosus (deoxygenated blood from the SVC is expelled into the pulmonary artery and ductus arteriosus o the lower body of the fetus)
blood entering the fetus through the umbilical vein is conducted via what shunt into the IVC?
ductus venosus
what do you use to keep a patent PDA open?
prostaglandins (3 P's)
the umbilical vein becomes what structure postnatally?
ligamentum teres hepatis
the umbilical arteries become what structure postnatally?
mediaL umbilical ligaments
what is the postnatal correlate to the allantois?
mediaN umbilical ligament
what does the first aortic arch give rise to?
part of the maxillary artery (1st is MAXimal)
what does the second aortic arch give rise to?
stapedial and hyoid artery (Second-Stapedial)
the common carotid artery and proximal part of internal carotid are derived from which aortic arch?
3rd (c is 3rd letter of alphabet)
what structures does the 4th aortic arch give rise to?
on left - aortic arch; on right - proximal part of subclavian artery
what does the 6th aortic arch give rise to?
proximal part of pulmonary arteries and (on left only) ductus arteriousus
branchial arch 1 derivatives are supplied by what nerves?
CN V2, V3 (1, 2, 3)
branchial arch 2 derivatives are supplied by what nerve?
CN VII (2 II's)
CN IX supplies the derivatives of which branchial arch?
arch 3
branchial arches 4 and 6 are supplied by what nerve?
CN X (4+6=10) (4th arch - superior laryngeal branch, 6th arch - recurrent laryngeal branch)
all of the intrinsic muscles of the larynx are derived from the 6th branchial arch except what?
which branchial arches form the posterior 1/3 of tongue?
arches 3 and 4
which branchial arch makes no developmental contributions?
arch 5
which nerves are responsible for taste?
solitary nucleus - CN VII, IX, X
tongue sensation is supplied by which nerves?
CN V3, IX, X
motor innervation to the tongue comes from which nerve?
what does the first branchial cleft develop into?
external auditory meatus
what do the 2nd through 4th branchial clefts form and then what happens to them?
they form temporary cervical sinues but are obliterated by proliferation of 2nd arch mesnchyme
what can a persistent cervical sinus lead to?
a branchial cyst in the neck
the 1st branchial pouch develops into what?
endoderm-lined ear structures - middle ear cavity, eustachian tube, mastoid air cells
which branchial pouch does the epithelial lining of the palatine tonsil derive from?
2nd pouch
the inferior parathyroids develop from which branchial pouch?
3rd pouch (dorsal wings) - 3 is inferior to 4
the ventral wings of the 3rd pouch develop into what structure?
which branchial pouch do the superior parathyroids develop from?
4th pouch
aberrant development of 3rd and 4th pouches results in what syndrome?
DiGeorge's - leads to T-cell deficiency (thymic aplasia) and hypocalcemia (failure of parathyroid development)
what is the most common site for ectopic thyroid tissue?
cleft lip results from the failure of fusion of what?
maxillary and medial nasal processes (primary palate)
cleft palate results form the failure of fusion of what?
lateral palatine processes, the nasal septum, and/or median palatine process (formation of secondary palate)
what does the ventral pancreatic bud differentiate into?
pancreatic head, uncinate process (lower half of head), and main pancreatic duct
the spleen arises from dorsal mesentery but is supplied by artery of which gut?
the genital tubercle gives rise to what strucures?
glans penis, glans clitoris (3 g's)
what structure do the corpus spongiosum and vestibular bulbs arise from?
urogenital sinus
what is the female analogue of the bolbourethral glands (Cowper's), and what do they arise from?
greater vestibular glands (Bartholin's); urogenital sinus
which branchial arch supplies: mandible, malleus, incus, sphenomandibular ligament, muscles of mastication (temporalis, masseter, lateral and medial pterygoids), mylohyoid, anterior belly of digastric, tensor tympani, tensor veli, palatini, and anterior
branchial arch 1
which branchial arch supplies: stapes, styloid process, lesser horn of hyoid, stylohyoid ligament, muscles of facial expression, stapedius, stylohyoid, posterior belly of digastric?
branchial arch 2
what cartilage and muscle does branchial arch 3 supply?
greater horn of hyoid, stylopharyngeus (CN IX)
thyroid, cricoid, arytenoid, coniculate, and cuneiform cartilages are derivatives of which branchial arches?
branchial arches 4-6
most pharyngeal constrictors, cricothyroid, levator veli palatini are supplied by which branchial arch?
branchial arch 4
the superior laryngeal branch of CN X supplies which branchial arch?
4th branchial arch
the recurrent laryngeal branch of CN X supplies which branchial arch?
what placental component is derived from the mother rather than the fetus?
lacunar network
the omental bursa and greater omentum are derived from what?
dorsal mesogastrium, which is the mesentary of the stomach regoin
what does an ostium primum type of ASD result from
failure of the septum primum to fuse with the endocardial cushions
what does a sacrococcygeal teratoma arise from? what is it?
tumor that arises from remnants of the primitive streak (which normally disappears); more common in female infants; usually becomes malignant during infancy and must be removed before 6 mos.
what is a chordoma?
tumor that arises from remnants of notochord - may be found intracranially or in sacral region; usually occurs in men late in life
what is caudal dysplasia and what causes it?
constellation of syndromes ranging from minor lesions of vertebrae to complete fusion of lower limbs - caused by abnormal gastrulation
what causes tetralogy of fallot?
abnormal neural crest cell migration such that there is skewed development of the AP septum
list the four classic malformations associated with tetralogy of fallot
pulmonary stenosis, overriding aorta, VSD, RVH
what is the most common clinically significant ASD?
foramen secundum defect - caused by excessive resorption of septum primum, septum secundum, or both
what is the most common type of VSD?
membranous VSD
what is the cause of a membranous VSD?
faulty fusion of the right bulbar ridge, left bulbar ridge, and AV cushions
postductal coartctation of the aorta is commonly associated with what syndrome?
turner's syndrome (XO)
which crosses the placenta: IgM or IgG?
AFP is elevated in what type of defects?
neural tube - spina bifida, anencephaly
what is the cause of spina bifida occulta and how common is it?
defect in the vertebral arches (least severe variation; tuft of hair); occurs in 10% of the population
what causes spina bifida with meningocele?
occurs when the meninges project through a vertebral defect, forming a sac filled with CSF
what is a meningomyelocele?
meninges and spinal cord project through a vertebral defect, forming a sac
what is the most severe type of spina bifida?
spina bifida with myeloschisis - open neural tube that lies on surface of back
what is the result when the anterior neuropore fails to close?
anencephaly - most common defect seen in stillborn fetuses
what is an arnold-chiari malformation?
cerebellomedullary malformation in which caudal cerebellar vermis and tonsils and medulla herniate through the foramen magnum
why does arnold-chiari malformation result in hydrocephalus?
because the outlet foramina of the fourth ventricle are obliterated (obstructive hydrocephalus)
arnold-chiari malformation is commonly associated with what other defects?
lumbar meningomyelocele, platybasia, aqueductal stenosis
congenital deafness is associated with in utero exposure to what virus?
name five causes of congenital cataracts
rubella, toxoplasmosis, congenital syphilis, down syndrome, galactosemia (inborn metabolic error)
what is associated with polyhydraminos and tracheoesophageal fistula?
esophageal atresia
annular pancreas is associated clinically with what shortly after birth?
obstruction of duodenum
when does an accesory pancreatic duct develop?
when the proximal part of the dorsal bud duct persists and enters the duodenum at its own site
what happens when fetal islets are exposed to high blood glucose levels?
accelerated development of pancreatic islets; associated with increased birth weight
how does an omphalocele present in a newborn?
a light gray, shiny sac protruding from the base of the umbilical cord
when does an omphalocele occur?
when the intestines (midgut loop) fail to return to the abdominal cavity
meckel's diverticulum occurs when a remnant of what persists?
vitelline duct
what occurs when the vitelline duct remains open
vitelline fistula - may present with fecal discharge at the umbilicus
what is gastroschisis and when does it occur?
protrusion of the viscera - occurs when there is a defect in the ventral abdominal wall
what is malrotation of the midgut associated with clinically?
where is the appendix normally located in relation to the cecum and where is it located when it is retrocecal or retrocolic?
normally found on the medial side of the cecum; retrocecal/colic - located on posterior side of cecum or colon
during the canalicular period of lung development (wks 3-15), what develops?
respiratory bronchioles and terminal sacs (primitive alveoli); premature infants born at less than 20 wks gestation rarely survive
when does differentiation of type I and type II pneumocytes begin?
week 24; premature fetuses born b/w wk 25-28 can survive w/ intensive care - earliest period at which fetuses can survive
name two defects that pulmonary hypoplasia can be found in association with
congenital diaphragmatic hernia and bilateral renal agenesis
when does a pharyngeal fistula occur and where is it generally located?
occurs when pharyngeal pouch 2 and pharyngeal groove 2 persist - forms patent opening from the internal tonsillar area to the external neck; found along the anterior border of the SCM
what causes first arch syndrome?
lack of migration of neural crest cells into branchial arch 1 (treacher collins, pierre robin)
what happens when the ureteric bud fails to develop?
renal agenesis
what is the result of bilateral renal agenesis?
potter syndrome - oligohydraminos allows uterine wall to compress fetus: deformed limbs, wrinkly skin, abnormal facial appearance
why is normal ascent of the kidneys arrested with horseshoe kidney?
the fused portion gets trapped behind the IMA
when does duplication of the urinary tract occur?
when the ureteric bud prematurely divides before penetrating the metanephric mesoderm
what other malformation is associated with exstrophy of the bladder?
cyst found along the midline on a path from the umbilicus to the apex of the urinary bladder
urachyl cyst - remnant of allantois persists
of what origin are the primitive neuroblasts found in neuroblastoma?
neural crest
name the three classic areas described in wilms' tumor
stromal area, tightly-packed embryonic cells, small tubules
what causes hypospadias?
urethral folds fail to fuse completely, resulting in the external urethral orifice opening onto the ventral surface of the penis
what is the defect in osteogenesis imperfecta?
type I collagen
what protein is defective in marfan's?
chances of achondroplasia increase with what?
increasing paternal age
unusually flat abdomen, breathlessness, and cyanosis in a newborn may be signs of what?
congenital diaphragmatic hernia
on which side is a congenital diaphragmatic hernia most commonly found, and what causes it?
left posterolateral side; caused by failure of pleuroperitoneal membrane to develop
an infant who vomits when laid on its back may have what?
esophageal hiatal hernia - renders esophagogastric sphincter incompetent so that stomach contents reflux into esophagus
deletion in the short arm of chromosome 5 results in what?
cri du chat syndrome
deficits such as MR, microcephaly, heart defects, and cat-like cry are characteristic of what?
cri du chat syndrome
what is the chromosomal abdnormality associated with Prader-Willi syndrome?
deletion of band q12 on chromosome 15 (found in the father)
MR, hyperphagia, and hypogonadism are characteristics of what congenital syndrome?
what is the chromosomal abdnormality associated with angelman syndrome
deletion of band q12 on chromosome 15 (found in the mother)
what are characteristics of angelman syndrome?
severe MR, seizures, dystaxia
the triad of heart defects, cataracts, and deafness are associated with what viral agent?
MR, microcephaly, cerebral calcifications, blindness and chorioretinitis, and hepatosplenomegaly are associated with what fetal infection?
MR, hydrocephalus, microcephaly, microphthalmia, chorioretinitis, and intracranial calcifications are associated with what nonviral infection?
name some characteristics of congenital syphilis
MR, hydrocephalus, deafness, corneal opacity and blindness, abnormal teeth (Hutchinson) and bones
when given to pregnant women, what types of abnormalities can lithium cause in the fetus?
congenital anomalies of the heart and great vessels
MR, microcephaly, craniofacial defects, and nail and digital hypoplasia can result from in utero exposure to what anticonvulsant?
phenytoin (dilantin)
digeorge's syndrome, cardiac malformations, and hirschprung's all result from failure of migration of what type of cells?
neural crest cells
infant who becomes cyanotic while crying may have what?
persistent truncus arteriosus
what does a persistent truncus arteriosus result from?
failure of aorticopulmonary system to form
annular pancreas results from what abnormality?
rotation of the ventral pancreatic bud around the second part of the duodenum
the alar plate forms what part of the spinal cord?
dorsal - becomes sensory/afferent
the basal plate forms what part of the spinal cord?
ventral - becomes motor
90% of PKD cases are due to a mutation in what? what chromosome is it on?
APKD1 on chromosome 16
this autosomal dominant disorder is associated with polycystic liver disease, berry aneurysms, mitral valve prolapse
adult polycystic kidney disease
the juvenile form of PKD is inherited in what manner?
autosomal recessive
what is another name for familial hypercholesterolemia?
hyperlipidemia type IIA
heterozygotes (1:500) with familial hypercholesterolemia have approx. what cholesterol level?
homozygotes with familial hypercholesterolemia have approximately what cholesterol?
what is the defect in familial hypercholesterolemia?
defective or absent LDL receptor
marfan's results from a defect in what gene?
fibrillin - leads to CT disorders
what are the cardiac findings in marfan's?
cystic medial necrosis of aorta -> aortic incompetence and dissecting aortic anuerysms; floppy mitral valve
cafe-au-lait spots, neural tumors, lisch nodules, skeletal disorders (e.g. scoliosis), pheo, and increased tumor susceptibility are associated with what autosomal dominant disease?
neurofibromatosis type I (von Recklinghausen's disease)
on what chromosome is the defect in neurofibromatosis type I
long arm of chromosome 17 - 17 letters in van Recklinghausen
where is the gene responsible for neurofibromatosis type II?
NF2 gene on chromosome 22 (type 2 - 22)
what are the characteristics of neurofibromatosis type II?
bilateral acoustic neuroma, optic pathway gliomas, juvenile cataracts
what is the inheritance pattern of tuberous sclerosis?
autosomal dominant
what are the skin findings associated with tuberous sclerosis?
facial lesions - adenoma sebaceum, hypopigmented 'ash leaf' spots
cortical and retinal hamartomas, seizures, MR, renal cysts, and cardiac rhabdomyomas are associated with what AD disease?
tuberous sclerosis
what is the genetic deletion associated with von Hippel-Lindau disease?
deletion of VHL gene (tumor suppressor) on chromosome 3 - 3 words in VHL
hemangioblastomas of retina/cerebellum/medulla are associated with what AD disorder?
von Hippel-Lindau
about half of all patients with VHL develop what?
multiple bilateral renal cell carcinomas and other tumors
what is the genetic defect in Huntington's?
expansion of CAG repeats on chromosome 4 (CAG - Caudate loses ACh and GABA; hunting 4 food)
what are symptoms common in Huntington's?
depression, progressive dementia, choreiform movements, caudate atrophy, and decreased levels of GABA and ACh in the brain
on what chromosome is the deletion located in familial adenomatous polyposis?
chromosome 5 - 5 letters in polyp
in what autosomal dominant disorder do adenomatous polyps in the colon develop after puberty?
familial adenomatous polyposis
what is increased in hereditary spherocytosis?
in what fashion is spherocytosis inherited?
autosomal dominant
what is the defect in achondroplasia?
cell-signaling defect of FGF receptor 3 - dwarfism - short limbs but head and trunk are normal size (autosomal dominant)
how is cystic fibrosis inherited and where is the gene defect?
autosomal recessive; defect in CFTR gene on chromosome 7
what finding in sweat is diagnostic for CF?
increased concentration of Cl- ions
what drug is given to patients with CF to loosen mucous plugs?
how do you diagnose muscular dystrophies?
increased CPK and muscle biopsy
how is Duchenne's inherited? what kind of mutation occurs? what does it lead to?
X-linked; frame-shift mutation - deletion of dystrophin gene - accelerated muscle breakdown
where does muscle weakness begin in Duchenne's?
pelvic girdle muscles and progresses superiorly
why does pseudohypertrophy of calf muscles occur in Duchenne's? what CV abnormality can occur?
fibrofatty replacement of muscle; cardiac myopathy
what is the genetic defect in Fragile X?
X-linked defect affecting the methylation and expression of the FMR1 gene - triplet repeat disorder (CGG)n
what syndrome is associated with macro-orchidism, long face with large jaw, large everted ears, and autism?
Fragile X
name 4 trinucleotide repeat expansion diseases
Huntington's, myotonic dystrophy, Friedrich's ataxia, fragile X (try hunting for my fried eggs)
what is the most common cardiac malformation in Down syndrome?
septum primum-type ASD due to endocardial cushion defects
MR, flat facial profile, prominent epicanthal folds, simian crease, duodenal atresia, and congenital heart disease are associated with what syndrome?
Down syndrome
people with Down syndrome are at increased risk for developing what leukemia?
95% of cases of Down syndrome are due to what?
meiotic nondisjunction of homologous chromosomes associated with advanced maternal age (from 1:1500 women under 20 to 1:25 in women over 45)
what percent of cases of Down syndrome are due to robertsonian translocation, and what percent are due to Down mosaicism (no maternal association)
4%; 1%
severe MR, rocker bottom feet, low set ears, micrognathia (small jaw), congenital heart disease, clenched hands, prominent occiput are associated with what syndrome?
Edward's - trisomy 18
severe MR, microphthalmia, microcephaly, cleft lip/palate, abnonrmal forebrain structures, polydactyly, congenital heart disease are found in what syndrome?
Patau's syndrome - trisomy 13
46, XX or XY, 5p-
cri du chat - deletion of short arm of chromosome 5 (cri du has 5 letters)
microcephaly, severe MR, high pitched crying, epicanthal folds, and cardiac abnormalities are found in what syndrome?
cri du chat
variable presentation as DiGeorge syndrome or velocardiofacial syndrome is associated with what chromosomal abnormality?
microdeletion at chromosome 22q11
developmental retardation, microcephaly, facial abnormalities, limb dislocation, and heart and lung fistulas are associated with what syndrome?
fetal alcohol syndrome
what is the number one cause of congenital malformations in the U.S.?
fetal alcohol syndrome
defects seen in fetal alcohol syndrome may occur as a result of what?
inhibition of cell migration
where is the break point in Fragile X?
q27.3 on X chromosome
the test for this condition involves culturing lymphocytes in a folate-deficient medium or with chemical agents such as methotrexate that tend to break chromosomes?
fragile X
the onset of preeclampsia before week 20 is suggestive of what?
hyatidaform mole
this chromosomal defect is the most common of those causing spontaneous abortions
trisomy 16
what 4 trisomies can be seen in live births?
8, 13, 18, 21
what is the only lipid storage disease that is X-linked?
Fabry's disease
uniparental disomy for chromosome 15 can cause what syndrome?
what is type I familial dyslipidemia?
what is increased in type I/hyperchylomicronemia?
blood TG, cholesterol levels
what is the deficiency in type I/hyperchylomicronemia?
lipoprotein lipase deficiency or altered apo C-II
what is type IIb familial dyslipidemia?
combined hyperlipidemia
what is incresed in combined hyperlipidemia?
what is the defect in combined hyyperlipidemia?
hepatic overproduction of VLDL
what is type III familial dyslipidemia?
what is increased in dysbetalipoproteinemia? what is elevated in blood?
TG, cholesterol
what is the pathophysiology of type III/dysbetalipoproteinemia?
altered apo E
what is increased in type IV/hypertriglyceridemia? what is elevated in blood?
what is the pathophysiology of hypertriglyceridemia?
hepatic overproduction of VLDL
what is increased in type V/mixed hypertriglyceridemia? what is elevated in blood?
VLDL, chylomicrons, TG, cholesterol
what is the pathophysiology of type V/mixed hypertriglyceridemia?
increased production/decreased clearance of VLDl and chylomicrons
follicular and undifferentiated lymphomas
breast, ovary, stomach cancer
small cell lung cancer
what is pleiotropy?
one gene has more than one effect on an individual's phenotype
when are Barr bodies seen?
any individual with 2 X chromosomes
what is variable expression?
nature and severity of phenotype varies from 1 individual to another
what is incomplete penetrance?
not all individuals with a mutant genotype show the mutant phenotype
whatis imprinting?
differences in phenotype depend on whether the mutation is of maternal or paternal origin (e.g. angelman's - maternal; prader-willi - paternal)
what is it called when a the severity of a disease worsens or age of onset of disease is earlier in succeeding generations?
what is loss of heterozygosity?
if a patient inherits or develops a mutation in a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer develops - not true for ongogenes
what is a dominant negative mutation?
exerts a dominant effect - a heterozygote produces a nonfunctional altered protein taht also prevents the normal gene product from functioning
what is linkage disequilibrium?
tendency for certain alleles at 2 linked loci to occur together more often than expected by chance - measured in a population, not a family, and often varies in different populations
what is mosaicism?
occurs when cells in the body have different genetic makeup - e.g. lyonization - random X inactivation in females
what is locus heterogeneity?
mutations at different loci can produce the same phenotype (e.g. albinism)
if a population is in Hardy-Weinberg equilibrium, then disease prevalence equals what?
p2 + 2pq + q2 = 1
if a population is in Hardy-Weinberg equilibrium, then what does allele prevalence equal?
p + q = 1
for Hardy-Weinberg - p and q are separate alleles: what does 2pq equal?
heterozygote prevalence
hypophosphatemic rickets is inherited in what manner?
X-linked dominant - transmitted through both parents - either male or female offspring of the affected mother may be affected, while all female offspring of the affected father are diseased
name 2 diseases with mitochondrial inheritance
Leber's hereditary optic neuropathy; mitochondrial myopathies
what is heteroplasmy?
presence of normal as well as mutated mitochondrial DNA
what is nondisjunction?
failure of separation of chromosomes
what is a balanced translocation?
occurs when non-homologous chromosomes exchange genetic material in such a way that no critical genetic material is lost

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