W01_04 Clinical cytogenetics 1 Flashcards
newborn presents with upslanting palpebral fissues + epicanthal folds, thickened tongue, nuchal thickness, hypotonia, simian crease, ventricular septal defect. what is the diagnosis?
down syndrome
how many base pairs of DNA in human genome?
3 billion 3x10^9
define chromatin
DNA, when uncondensed
define karyotype
an organized array of chromosomes in order of size and shape. can visualize banding patterns
define metacentric chromosome
centromere roughly in the centre
define submetacentric chromosome
centromere slightly above centre
define acrocentric chromosome
centromere at tip
note: chromosomes are treated with trypsin, then Giemsa stain to visualize the G bands
ok
light G bands are made of which bases?
G/C;
dark G bands are made of which bases?
A/T
47, XY, +21 is the cytogenic nomenclature for what?
down syndrome. “trisomy 21”
define aneuploidy
any chromosome number that’s not 46 (2n = euploid)
what’s the significance of M1 meiosis?
genetic shuffling and recombination
what’s the significance of M2 meiosis?
split into 23 chromosomes for germ cells
recall nondisjunction
can occur in M1 or M2 phases
note: trisomy 21 has a higher chance when mothers >30
ok
47, XXY is what?
klinefelter syndrome - tall, narrow shoulders, small testes, gynecomastia, testosterone deficiency, azoospermia
why is turner’s syndrome more rare than other sex chromosome aneuploidies?
has a higher miscarriage rate
what is typical of turner’s syndrome in utero, seen by ultrasound?
cystic hygroma, just behind the neck
mental retardation, failure to thrive, severe malformation of the heart, hypertonia, low-set ears, short sternum, clenched fists+overlaping digits, rocker-bottom feet are signs of which aneuploidy?
trisomy 18
growth retardation, severe mental retardation, CNS malformations (arhinencephaly, holoprosencephaly, microcephaly, microphthalmia), cleft lip/palate, polydactyly are signs of which aneuploidy?
trisomy 13. low chance of survival past perinatal period
digynic and diandric refer to what?
extra set of chromosomes from the father (diandric) or the mother (digynic) in triploidy
where can we samples cells for chromosome studies?
peripheral blood, bone marrow, lymph node, amniotic fluid, chorionic villi
when is amniocentesis performed?
16-18 weeks gestation
when is chorionic villus sampling performed?
10-12 weeks gestation
what’s germline mosaicism?
when there’s a genetic change in one of the cells that produces two or more genetically different cell lines in a person
somatic mosaicism is often associated with what?
malignancy
