Cytogenetics 1 Flashcards

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1
Q

Earliest you can get amniocytes from amniotic fluid for gross chromosome morphology studies

A

16-20 weeks gestation

to early risks maternal cell contamination

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2
Q

What can be done if you want to test prenatal cytogenetics before 16-20 weeks?

A

Chorionic villus sampling at 9-11 weeks

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3
Q

Abnormal chromosome dosage in a cell

A

Aneupoidy (trisomy and monosomy; partial addition or loss of matrial)

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4
Q

One or more complete sets of chromosomes

A

Euploidy (diploid, triploid, tetraploid; multiples of 23)

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5
Q

Mechanism and probability for polyploidy (triploid)

A

3 % of pregnancies

Dispermy (66%)
Meiotic failure (gamete stayed at 2n rather than 1n)
- Spermatogenesis (24%)
- oogenesis (10%)

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6
Q

Endomitosis

A

Failure to complete first zygotic division. (DNA replicated to become 4C, but cell division did not take place).

Very rare, always lethal results in tetraploidy.

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7
Q

Additional sex chromosomes

A

47 xxx
47 xxy
47 xyy

All experience relatively minor problems and live normal lives

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8
Q

Lacking sex chromosomes

A

45y is never viable
45x is turner syndrome
- 99% abort

Turners that survive:

  • Normal intelligence
  • Infertile
  • Minor physical diagnostic characteristics
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9
Q

Autosomal aneuploidy

A

Nullisomy (missing pair of homologs), monosomy (missing one chromosome), and trisomy are usually lethal (except 13, 18, 21).

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10
Q

Structural Abnormalities: Unbalanced Chromosomal Rearrangements

A

Most often associated with:

  • inversions
  • translocations (reciprocal, robertsonian)
  • insertions

Usually a normal phenotype but pose a risk to future generations because crossing over is not aligned correctly

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11
Q

Structural Abnormalities: Balanced Chromosomal Rearrangements

A

Most have normal phenotype unless the breakpoints disrupt a gene or some region of sequence gets deleted during the process of breaking and rejoining (becomes unbalanced)

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12
Q

Reciprocal Translocation Consequences for Gamete Formation

A

Pairing of translocation products to form quadrivalents

Major segregation products of meiosis are:

  • alternate (normal/balanced)
  • adjacent 1 (two unbalanced)
  • adjacent 2
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13
Q

Robertsonian Translocation

A

Translocation between two acrocentric chromosomes resulting in loss of the short arms of both chromosomes, but does not affect the DNA content of long arms

During meiosis form trivalent configuration

  • seg products produces normal/balanced gametes
  • monsomies and trisomies
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14
Q

Structural Abnormalities: Inversions

A

Paracentric:
50% balanced
50% inviable (one acentric and other dicentric)

Pericentric:
50% balanced
50% unbalanced

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