Chromosomes

Question 1

How are autosomes numbered?

Answer 1

In order (supposedly) of decreasing size

Question 2

What are chromosomes stained with to show alternating light and dark bands?

Answer 2

Giemsa

Question 3

Explain Xp21.2

Answer 3

X chromosome
P arm = Short arm
2 main band 
1 sub-band 
.2 sub-sub-band

Question 4

How are bands numbered?

Answer 4

According to increasing distance from the centromere

Question 5

What is Karyotype?

Answer 5

Description of chromosome set

Question 6

What is Karyogram (ideogram)?

Answer 6

Depiction of chromosome set

Question 7

How is karyotype recorded?

Answer 7

Number of chromosomes, identity of sex chromosomes, anomalies

Question 8

45, X is the karyotype of what?

Answer 8

Turner Syndrome

Monosomy X

Question 9

47, XX, +21 is the karyotype of what?

Answer 9

Female with Down syndrome

Trisomy 21

Question 10

69, XXY is the karyotype of what?

Answer 10

Triploid male

Question 11

46, XY, del(5p) is the karyotype of what?

Answer 11

Cri di chat Syndrome

Male with deletion of short arm of chromosome 5

Question 12

46, XX, t(9;22)(q34;q11) is the karyotype of what?

Answer 12

Cells from female with translocation between chromosome 9, q34 and chromosome 22, q11

Question 13

Can a karyotype reveal a numerical as well as structural abnormalities?

Answer 13

Yes

Question 14

What is aneuploidy?

Answer 14

Presence of extra INDIVIDUAL chromosome(s)

or absence of chromosome(s) due to non-disjunction during meiosis

Question 15

Examples of aneuploidy

Answer 15

Monosomy (absence of a chromosome, 1 chromosome instead of 2)
Disomy (2 copies of a chromosome, should only be 1 in a gamete)
Trisomy (extra chromosome, 3 copies instead of 2)

Question 16

What is polyploidy?

Answer 16

Extra SET(s) of chromosome(s)

Question 17

How is Down Syndrome brought about?

Answer 17

Fertilisation of a normal gamete with a disomic gamete (2 copies of 1 chromosome)

e. g. Down syndrome is inevitable if parent (healthy carrier) has a robertsonian translocation of chromosome 21
e. g. possibility of Down syndrome if parent has a robertsonian translocation between chromosome 14 and 21

Question 18

What would occur if a nullisomic gamete (contains NO chromosome 21) is fertilised with a normal gamete?

Answer 18

Monosomy 21 (only 1 copy)
Lethal - would not survive

Question 19

What is trisomy 18 called?

Answer 19

Edwards syndrome

Question 20

What is trisomy 13 called?

Answer 20

Patau syndrome

Question 21

What is XXY called?

Answer 21

Klinefelter syndrome

Question 22

Consequences of tuner syndrome

Answer 22

Short stature, infertility due
to incomplete ovarian
development
Approx. 10%
risk of coarctation of the
aorta
Normal intelligence
and almost normal life expectancy

Question 23

Consequences of Klinefelter syndrome

Answer 23

Tall, infertile, possible
poorly developed
secondary sexual
characteristics, possible slight reduction in IQ

Question 24

Consequences of 47XYY or 47XXY

Answer 24

Tall

Possible slight reduction in IQ

Question 25

Why do extra X chromosomes not make much difference?

or lack of 1 X in a female

Answer 25

X chromosome inactivation

Regardless of how many X chromosomes present, only 1 is activated

Question 26

List possible structural abnormalities

Answer 26

Deletions e.g. Cri du chat syndrome - deletion of short arm
Duplications
Inversions - usually no medical problems
Translocations
Ring chromosomes

Question 27

Reciprocal translocation

Answer 27

Exchange of material between non-homologous chromosomes

Usually no harmful effects as no loss/ gain of material

Question 28

Robertsonian translocation

Answer 28

Fusion between long arms of afrocentric chromosomes with loss of short arms
Risk of loss/gain of material in gametes

Question 29

Non-invasive parental diagnosis of common aneuploidies

Answer 29

Quadruple test, biochemical markers in maternal circulation
Analysis of nuchal translucency by ultrasound
Detects 90% of Down syndrome
1:6 true:false positives, high false positive rate

Question 30

Invasive parental diagnosis of common aneuploidies

Answer 30

Amniocentesis

Chromosome analysis

Question 31

What is the name given to reciprocal translocation between chromosome 9 and 22 present in >90% of chronic myeloid leukaemia?

Answer 31

Philadelphia chromosome

Question 32

What are the letters for long/ short arms?

Answer 32

P - short (petite)

Q - long (queue)

Question 33

Name to describe centromere near centre but not in the middle?

Answer 33

Sub-metacentric

Question 34

Name to describe centromere in the middle?

Answer 34

Metacentric

Question 35

Name to describe centromere near end of chromosome?

Answer 35

Acrocentric