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Clinical Cytogenetics and Molecular Genetics > Sex Chromosomes > Flashcards

Sex Chromosomes Flashcards

1
Q

What is the rough incidence of X and Y aneuploidy in newborns?

A

1 in 500 (475)

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2
Q

What is the incidence of all chromosome abnormalities in newborns?

A

1 in 150 (154)

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3
Q

What is the incidence of aneuploidy in newborns (sex chromosomes and autosomes)?

A

1 in 250 (263)

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4
Q

What is the incidence of autosome aneuploidy in newborns?

A

1 in 700

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5
Q

A. What is the incidence of total structural chromosome abnormalities in newborns?
B. What is the incidence of balanced structural chromosome abnormalities in newborns?
C. What is the incidence of unbalanced structural chromosome abnormalities in newborns?

A

A. 1 in 400 (375)
B. 1 in 500
C. 1 in 1600

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6
Q

Sample type for numerical sex chromosome analysis?

A

Buccal smears

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7
Q

Sex chromosome body discovered in 1949?

A

Barr body (Mike Bertram and Murray Barr)

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8
Q

What is Ohnos law?

A

Evolutionary conservation of genes on the X chromosome (1959)

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9
Q

X inactivation center gene (___) at Xq13.2 that initiates X inactivation

A

XIST - x inactive transcript = non-coding transcript and functional RNA

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10
Q

X inactivation spreads from the ____?

A

XIC- X inactivation center

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11
Q

X inactivation and Barr body occurs about day ____ during the _____ stage of early embryonic development

A

16, blastocyst (hollow ball of 50-150 cells)

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12
Q

Explain exceptions when X-inactivation is not random:
1. ______ abnormal chromosomes
2. ______ X chromosome in extraembryonic membranes

A
  1. structurally
  2. paternal
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13
Q

Is X inactivation complete?

A

No
(pseudoautosomal region - functional homolog on the Y and 15% X genes) - lack CpG islands

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14
Q

Is X inactivation permanent?

A

No.
-Reversed in development of germ cells (not passed on to gametes)

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15
Q

Inactive X chromosome enriched for histone _____

A

macroH2A

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16
Q

Compare active vs inactive X replication in S phase

A

Active X - early S phase with autosomes
Inative X -late S phase

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17
Q

50% of genes on the _____ arm of X escape inactivation

A

p (Xp)

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18
Q

There are approximately ____ genes on the X chromosome

A

900 (800-900)

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19
Q

There are approximately ____ genes on the Y chromosome

A

50 (50-60)

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20
Q
  1. The _____ is the terminal 2.6 MB of Xpter and Ypter.
  2. The _____ is the terminal 320 KB of Xqter and Yqter.
A
  1. PAR1
  2. PAR2
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21
Q

1.____% of genes on X and 2. ___% of genes on autosomes encode genes related to intellectual ability

A
  1. 10%
  2. 3%
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22
Q

Klinefelter Syndrome Nomenclature

A

47, XXY

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23
Q

Klinefelter Phenotype

A

Tall
Hypogonadism
Atrophic testis and infertility
Underdeveloped secondary sexual characteristics
Learning disabilities
High risk metabolic syndrome
48, XXYY cause increase mental disabiluity

24
Q

1.Klinefelter origin is in Meiosis ___.
2. Which parent (%) and cause?

A
  1. Meiosis I.
  2. 50% Paternal — failure of Xp/Yp recombination in PAR1
    50% Maternal —40% Meiosis I and maternal age defect
25
Q

___% of Klinefelter individuals are mosaic. Cause?

A

15%. Postzygotic loss of one X copy.
Can be fertile

26
Q

Klinefelter incidence?

A

1/1000 (1 in 650 to 1 in 1000)

27
Q

Incidence, phenotype and cause of 47, XYY?

A

-1 in 1000 (like Klinefelter)
- little noticeable phenotype but behavior disorders - fertile
- Paternal meiosis II producing YY sperm

28
Q

Triple X Syndrome Karyotype

29
Q

Triple X Phenotype

A

Variable
- Neonatal hypotonia
- Somewhat tall
- Clinodactyly
- Fertile
- Learning deficits

30
Q

Triple XXX Mechanism

A

50-60% maternal meiosis I non-disjunction

31
Q

Turner syndrome Karyotype

32
Q

Turner syndrome phenotype

A

Short stature 100%
Redundant nuchal folds/lymphedema
Cardiovascular anomalies 30% (coarctation)
Streak ovaries and infertility

33
Q

Turner syndrome Incidence
At birth vs Conceptions

A
  1. Birth 1 in 2000 (to 1 in 5000)
  2. Conceptions 1-2 in 100 (95-99% of SABSs before week 28)
34
Q

Most common abnormality in spontaneous abortions (SABs) *95-99% of SABs before week 28

A

Turner syndrome 45, X

35
Q

Liveborn Turner syndrome may have confined ____ mosaicism for a normal cell line

36
Q

85% of Turner syndrome individuals maintain the paternal or maternal X?

37
Q

Approximately 10-12% of Turners syndrome are mosaic for normal or abnormal ____ cell line

A

Y - mixed gonadal dysgenesis
Usually male phenotype
mos 45,X[13]/46,XY[7] Male Karyotype / Female Habitus

38
Q

Turner syndrome individuals with mosaic normal or abnormal Y cell line are at risk for which tumor?

A

Gonadoblastoma (gonadal tumor)
*therefore rule out Y chromosomes with 45,X detected

39
Q
  1. X-aneuploidy (gain and loss) observed in 2-10% of blood cells in ___% of women of reproductive age. 2. Sample type to confirm age-related loss?
A
  1. 16%
  2. Buccal
40
Q

Gains of which sex chromosome is found in neoplasia

41
Q
  1. Low level Y chromosome loss may be associated with what? 2. Associated with what substance use?
A
  1. Morbidity and mortality
  2. Smoking/nicotine
42
Q

What are considered as Turner syndrome variants?

A

X structural abnormalities - most commonly deletions of Xp and Xq
*preferentially inactivated
*males not viable

43
Q

Karyotype for the following X variants:
1. isochromosome X
2. X del
3. ring X
4. marker X

A
  1. 45, Xi(X) = 15-18%
  2. 46, Xdel(X) = 2-5%
  3. 46, Xr(X) = 7-16%
  4. 46, Xm(x) = 7-16%
  • mosaic 7-16%
    *45% 45, X
44
Q

X region and genes associated with Turner syndrome phenotype (stature and ovarian function)

A
  • Xp (Xp11.2-p22)
  • SHOX (homeobox gene ) in PAR1 on X and Y - statute
  • Xq (Xq24) ovarian failure
45
Q

Name two syndromes of haploinsufficiency of SHOX (deletions in Xp22 or Yp11.3 - PAR1)

A
  1. Langer mesomelic dysplasia
  2. Leri-Weill dyschondrosteosis -
    *idiopathic short stature - pt mutation in SHOX
    *mild phenotype: SHOX-related short stature
46
Q

46,X,i(X)(q10) and mos 45,X/46,X,i(X)
from ___ exchange?

47
Q

Individuals with smaller marker chromosomes have a worse phenotype without the presence of the ____ gene (hint FISH test)

48
Q

Der(X) is always _____ (inactive or active) in balanced but favors the least imbalance in unbalanced translocations with XIST present?

A

Active - no XIC

48
Q

Der(X) phenotype?

A
  • IUGR
  • Respiratory distress
  • Left nare stenosis
  • Dysmorphic features
49
Q

Phenotype of deletions of SRY on Yp11.3

A

Sex determining regions
46,XY female habitus with gonadal dysgenesis
*SRY activated SOX9

50
Q

46, XX males have ?

A

cryptic X;Y translocation

51
Q

Deletions of Yq11.2 gene and phenotype?

A

DAZ
- infertility and azoospermia

52
Q

Deletions of Yq12 phenotype

A

None - heteromorphic variant (SATIII probe)

53
Q

Inheritance and phenotype of 46, X, idic(Y)(q11.2)

A

De novo
-mitotically unstable - can be seen with 45, X cell line
-varied phenotype with infertility and risk for gonadal tumors

54
Q

Common Y; Autosome translocation

A

der(15)t(Y;15)(q12;p12)

55
Q

Leri- Weill Dyschondroosteosis

A
  1. Short stature
  2. Mesomelia
  3. Madelung deformity
    **usually also includes STS gene

Clinical Cytogenetics and Molecular Genetics (21 decks)

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