W01_04 Clinical cytogenetics 1 Flashcards Preview

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Flashcards in W01_04 Clinical cytogenetics 1 Deck (27)
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1
Q

newborn presents with upslanting palpebral fissues + epicanthal folds, thickened tongue, nuchal thickness, hypotonia, simian crease, ventricular septal defect. what is the diagnosis?

A

down syndrome

2
Q

how many base pairs of DNA in human genome?

A

3 billion 3x10^9

3
Q

define chromatin

A

DNA, when uncondensed

4
Q

define karyotype

A

an organized array of chromosomes in order of size and shape. can visualize banding patterns

5
Q

define metacentric chromosome

A

centromere roughly in the centre

6
Q

define submetacentric chromosome

A

centromere slightly above centre

7
Q

define acrocentric chromosome

A

centromere at tip

8
Q

note: chromosomes are treated with trypsin, then Giemsa stain to visualize the G bands

A

ok

9
Q

light G bands are made of which bases?

A

G/C;

10
Q

dark G bands are made of which bases?

A

A/T

11
Q

47, XY, +21 is the cytogenic nomenclature for what?

A

down syndrome. “trisomy 21”

12
Q

define aneuploidy

A

any chromosome number that’s not 46 (2n = euploid)

13
Q

what’s the significance of M1 meiosis?

A

genetic shuffling and recombination

14
Q

what’s the significance of M2 meiosis?

A

split into 23 chromosomes for germ cells

15
Q

recall nondisjunction

A

can occur in M1 or M2 phases

16
Q

note: trisomy 21 has a higher chance when mothers >30

A

ok

17
Q

47, XXY is what?

A

klinefelter syndrome - tall, narrow shoulders, small testes, gynecomastia, testosterone deficiency, azoospermia

18
Q

why is turner’s syndrome more rare than other sex chromosome aneuploidies?

A

has a higher miscarriage rate

19
Q

what is typical of turner’s syndrome in utero, seen by ultrasound?

A

cystic hygroma, just behind the neck

20
Q

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?

A

trisomy 18

21
Q

growth retardation, severe mental retardation, CNS malformations (arhinencephaly, holoprosencephaly, microcephaly, microphthalmia), cleft lip/palate, polydactyly are signs of which aneuploidy?

A

trisomy 13. low chance of survival past perinatal period

22
Q

digynic and diandric refer to what?

A

extra set of chromosomes from the father (diandric) or the mother (digynic) in triploidy

23
Q

where can we samples cells for chromosome studies?

A

peripheral blood, bone marrow, lymph node, amniotic fluid, chorionic villi

24
Q

when is amniocentesis performed?

A

16-18 weeks gestation

25
Q

when is chorionic villus sampling performed?

A

10-12 weeks gestation

26
Q

what’s germline mosaicism?

A

when there’s a genetic change in one of the cells that produces two or more genetically different cell lines in a person

27
Q

somatic mosaicism is often associated with what?

A

malignancy

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