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Clinical Cytogenetics and Molecular Genetics > Translocations > Flashcards

Translocations Flashcards

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1
Q

Translocations can allow for up to ___% of the genome to be trisomic (depending on the region)

A

4%

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2
Q

Translocations can allow for up to ___% of the genome to be monosomic (depending on the region)

A

2%

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3
Q

In translocations it is always recommended to study the ________ chromosomes

A

parental

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4
Q

Frequency of Robertsonian translocations

A

1 in 800/1000 (part of the balanced 1in 500 risk)

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5
Q

Acrocentric p arms account for _____ % of the genome

A

2.2%

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6
Q

Acrocentric chromosome distal satellite p13 arms contain up to 300 copies of _______ genes responsible for organizing the nucleolus

A

rRNA

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7
Q

Acrocentric chromosome distal satellite p12 region is known as the _________ ______ and comes before the p13 rRNA region

A

satellite stalk

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8
Q

5 acrocentric chromosomes

A

13, 14, 15, 21 and 22

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9
Q

_______ satellite family at centromeres of 1, 9, 13, 14, 15, 21, 22 and Y

A

beta

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10
Q

A ________ translocation (1916) involves two acrocentric chromosomes at the centromere where the derivative p arms are largely lost and two copies of q arms are observed

A

Robersonian

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11
Q

_____ - _____ % of trisomy 21 are Robertsonian translocations

A

4-5%

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12
Q

Derivative 21 mostly involve D chromosomes ____, _____ and _____ as the G chromosomes ______ and _____ are not viable

A

D = 13, 14, 15
G = 21 and 22

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13
Q

Most (75%) Robertsonian translocations involving 13, 14 and 15 are _____ ______ but up to 25% can be _______

A

de novo -75%
familial - 25%

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14
Q

Segregation of Robertsonian translocations occurs in meiosis ______ and involves the trivalent formation

A

metaphase I

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15
Q

Adjacent or alternate segregation patterns result in normal and balanced translocations?

A

Alternate

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16
Q

Almost all DS inherited from a familial der(14;21) is _______ (paternal/maternal) in
origin from error in meiosis ________

A

maternal, meiosis I

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17
Q

der(14;21) carriers
Risk of fetus with translocation trisomy 21,
− maternal carrier _____% at amniocentesis, about _______% at term

A

15%
10-12%

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18
Q

der(14;21) carriers
Risk of fetus with translocation trisomy 21,
− Paternal carrier, <____%

A

<1%

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19
Q

der(14;21) carriers
Risk of UPD14?

A

<1/2% for both maternal and paternal

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20
Q

True or false? The rare der(21;21) carrier or isochromosome 21q has essentially no chance of a chromosomally normal conception.

A

True

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21
Q

The rare der(21;21) carrier or isochromosome 21q is mechanistically the result of an error in meiosis _________?

A

meiosis I

22
Q

Trisomy 13 incidence in live births?

A

1 in 16,000

23
Q

Trisomy 13 life expectancy?

A

1 year

23
Q

Trisomy 13 phenotype?

A

heart defects
urinary malformations
* Dysmorphia:
- Polydactyly; clenched fist
- Small head and eyes
- Cleft lip/palate
- Rocker-bottom feet
– Holoprosencephally

24
Q

Most common (1 in 1300) chromosome structural rearrangement?

A

der (13;14)
rob (13;14)

25
Q

Incidence of rob/der (13;14)

A

1 in 1300

26
Q

Der (13;14) is _______% of all Robertsonian translocations

A

75%

27
Q

Maternal vs paternal risk of der (13;14) having offspring with unbalanced
karyotypes?

A

Maternal: 1%
Paternal: <1%

28
Q

There is an ___________risk of Robertsonian translocations in infertile men

A

increased

29
Q

Risk of UPD in der (13;14) translocations?

A

<1/2%

30
Q

der (14;15) prevalence?
der (13;15) prevalence?
der(15;15) prevalence?

A

der (14;15) = 5%
der (13;15) = 2%
der(15;15) = 2%

31
Q

Whenever chromosome ______ is involved in a Robertsonian translocation, parental chromosomes are recommended?

A

15

32
Q

Mechanism of der(15;15)?

A

Fusion in zygote at mitosis

33
Q

der (13;15) UPD with trisomy rescue mechanism?

A

Trisomy 15 with adjacent segregation followed by rescue by postzygotic loss of 15 (usually 15 UPD maternal)

34
Q

der (13;15) with residual trisomy?

A

Mosaic mitotic loss of trisomy 15 but usually with severe PWS phenotype

35
Q

Loss of paternal 15q11.2-q13?

A

Prader Willi Syndrome (20-30% UPDmat)

36
Q

Loss of maternal 15q11.2-q13?

A

Angelman syndrome (7% UPDpat)

37
Q

The most common recurrent non-Robertsonian translocation in humans ?

A

t(11;22)(q23;q11.2)

38
Q

The majority of t(11;22) are _________ (99%)

A

familial

39
Q

Risk in t(11;22) for SAB (maternal = paternal)

A

> 27%

40
Q

Risk in t(11;22) for liveborn with derivative: ____% mat, ___% pat

A

5%, maternal, 2-5% paternal

41
Q

Risk in t(11;22) for offspring to be balanced carrier maternal and paternal

A

maternal 55%
paternal 40%

42
Q

t(11;22) involves a _______ at 22q11.2 and an ______-rich region on 11q23

A

LCR on 22q11.2
AT-rich on 11q23

43
Q

PATRR = Palindromic AT-rich repeats form ______ _______

A

hairpin loops

44
Q

Deletions, duplications and translocations at 22q11 occur in greater than _______ live births

A

1/3000 – 4000

44
Q

The 22q11 region is a hotspot for _________ chromosomal rearrangements

A

nonrandom

45
Q

The 22q11 deletion syndrome includes

A

– DiGeorge,
– Velocardiofacial
– Conotruncal anomaly face syndromes

46
Q

22q duplications include

A

Cat Eye syndrome
* Supernumerary derivative chromosome 22
Emanuel syndrome
* duplication of 22q10-22q11 and duplication of 11q23-qter
on a supernumerary derivative chromosome 22

47
Q

Supernumerary +der(22)t(11;22)

A

Emanuel syndrome

48
Q

Supernumerary +der(22)t(11;22) phenotypes

A

conotruncal heart defects (cardiac outflow tract anomalies)
microcephaly
cleft palate
micrognathia
skin tags or pits
genital abnormalities in males
intellectual disability
* Features of both 11q trisomy (e.g. microcephaly) and trisomy 22
(e.g. imperforate anus

Clinical Cytogenetics and Molecular Genetics (20 decks)

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