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Foundations To Medicine 2 > Karyotype & Aneuploidy > Flashcards

Karyotype & Aneuploidy Flashcards

1
Q

What are the types of chromosomal abnormalities

A

Numerical chromosomal abnormalities May be a result from:

  • non-disjunction during meiosis
  • non- disjunction during mitosis
  • Mosaicism
Structural chromosomal abnormalities May arise from
-deletions
-duplications
-inversions
-translocations
Isochromosom3s
-ring chromosomes
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2
Q

How is a karyotype generated?

A
  1. Blood sample added to culture medium
  2. White blood cells, lymphocytes, divide in the presence of phytohemagglutinin
  3. Dividing cells arrested in metaphase with spindle inhibitor colchicine
  4. Cells swollen with hypoton8c solution
  5. Spread onto glass slide and fix
  6. Stain and examine with microscope
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3
Q

What is a karyotype?

A

These are analyzed by microscopy

  • only relatively large alterations will be observable by karyotype
  • banding pattern must be altered

Can detect deletions, duplications, inversions, translocations, other abnormalities

Deletions larger then 5 Mb are usually by standard karyotype (this is by microscopy)
-Deletions that aren’t visible by karyotype are called “Microdeletion”

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4
Q

Classify chromosome by structure

A
  1. Total. Length of the chromosome is equal on both ends of the chromosome from the centromere- metacentric
  2. Sub metacentric- p are shorter than q arms
  3. Acrocentric- only satellites on the p side
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5
Q

What are used to classify chromosomes?

A
  1. Total length of the chromosome
  2. position of the centromere
  3. Presence of satellites
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6
Q

How can we classify chromosomes by G-banding pattern?

A

Ideogram of the G-banding pattern of metaphase chromosomes stained with Geimsa

Resolution: can’t detect deletions or insertions smaller than 5Mb

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7
Q

What are FISH?

A

FISH are big; ASO probes are small

  • typically to get a good signal, they are about 100 kB or bigger
  • This allows a lot of fluorescent tags to be packed into the probe

With the correct probe FISH can detect:

  • numerical chromosome aberrations
  • deletions
  • translocations
  • gene amplification(very important in cancer characterization)

FISH May detect many “Microdeletions” because FISH is of higher resolution than G-band karyotype
-As long as the deletion is larger than the probe being used, the deletion can be detected

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8
Q

Contrast interphase FISH and metaphase FISH

A

Interphase FISH- rapid test, avoids need for cell culture, chromosomes are de condensed in the nucleus

Meta9hsse- must first culture the cells, usually done @fter a G-band karyotype (condensed metaphase chromosomes), gives location information because the banding pattern would be known

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9
Q

What is a chromosomal painting?

A

Chromosomal painting, spectral karyotype, SKY FISH
-Each chromosome probed so that it fluorescent a different color

Can show translocations and rearrangements

Very useful in cancer genetics- genetic stability in advanced cancer

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10
Q

Summarize chromosomal abnormalities

A

Chromosomal abnormalities account fir a large number of spontaneous abortions
-(non induced embryonic or fetal death or passage of products of conception before. 20 weeks gestation)

Chromosomal abnormalities May be

  • numerical
  • structural
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11
Q

What are the numerical chromosomal abnormalities?

A

Euploidy(polyploidy) (number of chromosomes is in multiples of 23)

  • Diploidy- normal human compliment of chromosomes
  • triploidy- contain three copies of each chromosome(69)- not compatible with life
  • tetraploidy- lethal- contain four copies of each chromosome (92)

Aneuplody-

  • Monosomy: loss of a chromosome
    • Nit compatible with life (except Monosomy X: Turner syndrome)
  • Trisomy: presence of an additional chromosome (only 3 are compatible with life)
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12
Q

What is aneuploidy?

A

Chromosome number isn’t a multiple of 23

  • Monosomy: loss of a chromosome. Nit compatible with life (except in Turner syndrome)
  • Trisomy: presence of an additional chromosome (frequently confused with triploidy(69 chromosomes)

Autosomal trisomy- Edward syndrome (18), Down syndrome, Patau syndrome(13)

Sex chromosome aneuploidy- (45,X) Turner, 47, XXY) kleinfekter sundrome

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13
Q

What are the risk factors of trisomy 21?

A

Most common live born autosomal trisomy

Risk factors: increased maternal age, increases risk of meiotic nondisjunction during oogenesis (most common is meiosis 1 nondisjunction)

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14
Q

WhAt are the features of trisomy 21?

A
  • intellectual” disability
  • short stature
  • depressed nasal bridge, unslanting palpebral fissures, epicantal folds
  • Cingenitak heart defects
  • single palmar crease
  • develop changesssimilar to Ahlzeimer’s disease at a relatively young age.
    • One if the genetic factors responsible fir Ahlzeimer’s is localized to chromosome 21(amyloid precursor protein (APP)
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15
Q

What is the main use of FISH probes?

A

Will work with interphase stage cells to allow rapid return of results

Prenatal diagnosis with maternal serum screening and ultrasound

Karyotype analysis or FISH with fetal cells is confirmatory

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16
Q

What are the genetic causes of down syndrome?

A

Trisomy 21- due to non-disjunction during meiosis.

Down syndrome May also result from R9bertsonian translocation

Some children may be mosaic- some cells gave trisomy 21; som3 other cells may have normal karyotupe

17
Q

What are the features of edwards syndrome?

A

Genetic mechanism is nondisjunction during oogenesis

Features:
-Clenched fist, overlapping of fingers

  • Rocker bottom feet
  • Congenital heart defects
  • Low set ears , small lower jaw (micrognathia)
  • Microcephaly
  • Intelkectual disability
18
Q

What is the list of features of Patau syndrome (+13)?

A

Most common genetic mechanism is nondisjunction during oogenesis

Features

  • polydactyly
  • cleft lip and palate
  • microphthalmia
  • Microcephaly
  • intellectual disability
  • cardiac anomalies (VSD or ASD)
19
Q

What are the common features of (45,X)/Turner syndrome?

A

X chromosome Monosomy- usually due to nondisjunction during spermatogenesis

  • Short stature
  • webbed neck, cystic hygrometer at birth (neck swelling)
  • Primary amenorrhea/no menstruation
  • Gonadal dysgenesis
  • ‘Streak’ ovaries
  • Lymphoedema of hands and feet
20
Q

Explain mosaic Turner syndrome

A

Many TS patients are mosaic

  • Some of their cells are 45, X
  • Other cells are 46,XX and 47,XXX (indicate mitotic nondisjunction during embryogenesis)

Cells with 45,X: have no Barr body (inactivated X-chromosome )(female with NO Barr bidy)

-Isichromosome X will also lead to Turner syndrome

21
Q

Contrast he not your and mosaic Turner syndrome

A

Mosaic Turner syndrome-

  • fertilized egg, 46,XX
  • Mitotic nondisjunction during embryogenesis
  • Some cells are 45,X others are 46,XX and 47, XXX
  • during a post-fertilization mitosis, one of the X chromosomes evicted during cell division

Phenotypic-

  • fertilized egg, 46, XX
  • Mitotic nondisjunction during embryogenesis
  • Some cells are 45, X others are 46, XY
  • Mosaic 45,X/46,XY are recommended fir oophorectomy due to risk of gonadoblastoma
  • during post fertilization mitosis, the Y chromosome is evicted during cell division
22
Q

What are the features of kleinfekters?

A

Genetic mechanism responsible for kleinfelter syndrome is nondisjunction during meiosis

-Some individuals may be mosaic (46XY/47XXY/48/XXXY)

Features:

  • Gyecomastia
  • Female distribution 9f hair
  • Infertility and testicular atrophy due to low levels of testosterone
  • Feminization of features
23
Q

What are the probability of each abeuplofy occurring?

A

Trisomy 21- 1/830 live births

47, XXY(kleinfelter)- 1/1000 live births

45,X(Turner) -1/4000 live births

Trisomy 18- 1/7,50l live births

Trisomy 13- 1/22,700 live births

24
Q

What is non-disjunction ?

A

The most common type in females is meiosis 1

  • Individuals with down syndrome usually have two maternal chromosomes 21 and one paternal chromosome 21
  • If two maternal chromosomes aren’t identical to each other, the non-disjunction occurred at meiosis 1 (that is they have different alleles )
  • If the two maternal chromosomes are identical, the non-disjunction occurred at meiosis 2(sister chromatids shown as two blue alleles)
25
Q

How can we draw out which type of nondisjunction occurred?

A

-47,XXY kleinfekter syndrome may be caused by nondisjunction during meiosis 1 or meiosis 2 in the mom, or nondisjunction during meiosis 1 in dad

  • 47, XYY fetus is the result of meiosis 2 nondisjunction in dad
    • May not be caused by meiotic non-disjunction in the mom (hint: thus person is also)
  • 47, XXX females may be the result of meiosis 1 or 2 nondisjunction in moms or meiosis 2 non-disjunction in dad
    • may not be caused by meiosis 1 nondisjunction in dad
26
Q

What is Mosaicism?

A

The presence of two or more populations of cells in one individual with different genotypes

Mixed somatic/germline mosaic
Some percentage of the cells in a person body are of one genotype, and other cells are of another genotype

Confined germline mosaic
All cells in the body are of one genotype
Cells of the gametes are something else (leads to high risk of having children with a genetic disorder)

27
Q

What are the two ways could be mosaic for down syndrome ?

A
  1. Non-disjunction May occur as a post-zygotic event during embryonic development; that is mitotically (after fertilization of a normal ovum and normal sperm)

This will lead to 2 cell types:

  • one continues as normal karyotype
  • the other with trisomy 21
  1. Trisomy rescue- nondisjunction May occur in the ovum during oogenesis, and fertilization by a normal sperm loads to trisomy 21 in the conception
    - During a post-fertilization mitosis, one of the extra chromosone 21 is evicted during cell division
    - Now the fetus has 2 cell types, one with normal karyotype, and one that is trisomy 21

Foundations To Medicine 2 (37 decks)

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