W01_04 Clinical cytogenetics 1

Question 1

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

Answer 1

down syndrome

Question 2

how many base pairs of DNA in human genome?

Answer 2

3 billion 3x10^9

Question 3

define chromatin

Answer 3

DNA, when uncondensed

Question 4

define karyotype

Answer 4

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

Question 5

define metacentric chromosome

Answer 5

centromere roughly in the centre

Question 6

define submetacentric chromosome

Answer 6

centromere slightly above centre

Question 7

define acrocentric chromosome

Answer 7

centromere at tip

Question 8

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

Answer 8

ok

Question 9

light G bands are made of which bases?

Answer 9

G/C;

Question 10

dark G bands are made of which bases?

Answer 10

A/T

Question 11

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

Answer 11

down syndrome. “trisomy 21”

Question 12

define aneuploidy

Answer 12

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

Question 13

what’s the significance of M1 meiosis?

Answer 13

genetic shuffling and recombination

Question 14

what’s the significance of M2 meiosis?

Answer 14

split into 23 chromosomes for germ cells

Question 15

recall nondisjunction

Answer 15

can occur in M1 or M2 phases

Question 16

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

Answer 16

ok

Question 17

47, XXY is what?

Answer 17

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

Question 18

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

Answer 18

has a higher miscarriage rate

Question 19

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

Answer 19

cystic hygroma, just behind the neck

Question 20

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?

Answer 20

trisomy 18

Question 21

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

Answer 21

trisomy 13. low chance of survival past perinatal period

Question 22

digynic and diandric refer to what?

Answer 22

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

Question 23

where can we samples cells for chromosome studies?

Answer 23

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

Question 24

when is amniocentesis performed?

Answer 24

16-18 weeks gestation

Question 25

when is chorionic villus sampling performed?

Answer 25

10-12 weeks gestation

Question 26

what’s germline mosaicism?

Answer 26

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

Question 27

somatic mosaicism is often associated with what?

Answer 27

malignancy