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Mcb1 > Chromosomes And Cytogenetics > Flashcards

Chromosomes And Cytogenetics Flashcards

1
Q

What are chromosomes?

A

Complex structures of DNA, his tone proteins and non-his tone proteins

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2
Q

What is a common cause of infertility no recurrent miscarriage?

A

Chromosome abnormalities

  • 50% of 1st trimester
  • multiple congenital anomalies in ~0.5% of newborns
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3
Q

What is polyploidy?

A

Changes in the number of all chromosomes equally

E.g. Triploidy, tetraploidy

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4
Q

What is Aneuploidy? (~1 in 300 new burns)

A

Changes in number of one or multiple chromosomes unequally

E.g. Monosomy, trisomy, retraso y

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5
Q

What numerical abnormalities are compatible with life?

A

13, 18 and 21 (trisomy)

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6
Q

How can triploidy occur?

A

66% 2 xsperm and 1 egg
10% 1 sperm and a 2n egg
24% a 2n sperm and an egg

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7
Q

How does tetraploidy occur?

A

Endomitosis

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8
Q

What 3 types of structural abnormalities occur in chromosomal structures?

A
  1. Balanced
  2. Unbalanced
  3. Aneuploidy (numerical abnormality)
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9
Q

What are the kinds of balanced structural chromosomal abnormalities?

A
  1. Translocation
  2. Inversion

-This is relocation of genetic material

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10
Q

What are the kinds of unbalanced chromosomal structural abnormalities?

A
  1. Duplication

2. Deletion

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11
Q

What are the kinds of Aneuploidy chromosomal abnormalities?

A
  1. Gain of genetic material

2. Loss of genetic material.

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12
Q

What is the common name of 22q11 deletion?

A

DiGeorge Syndrome

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13
Q

What test is ordered for karyotyping?

A

FISH

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14
Q

What are some signs and symptoms of Down syndrome?

A

Floppy baby (hypotonia)
Excess nuchal skin
Bilateral single palmar crease (simian)

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15
Q

What is the karyotype for Down syndrome?

A

47,XX+21

47,XY+21

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16
Q

What are some causes of Down syndrome?

A

95% complete trisomy 21 (Meosis)
4% are robertsonian translocation
1% are mitotic nondisjunction (milder features)

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17
Q

What are some clinical features of Down syndrome?

A 
Nuchal skin
Brachycephaly
Flat occiput
Epicanthic folds 
Smaller ears with over-folded helix
Palpebral folds
Atresia 
Heart problems
Strabismus-alignment of eyes
Hirschsprung disease
(Just recognize them don't memorize all)q
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18
Q

What is Hirschspring disease?

A

Blockage of the Large intestine

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19
Q

What is the is of a Down syndrome patient?

A

25-50

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20
Q

What are Down syndrome patients at a higher risk of developing?

A
  • leukemia (ALL or AML) 10-20 times increased risk
  • Alzheimer disease at age 40

40% congenital heart disease
-septal defect

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21
Q

What is nondisjunction?

A

Failure of chromosomes or chromatids to segregate in M1 or M2

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22
Q

If nondisjunction occurred in Meosis 2 what is seen?

A

Chromosomes are identical

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23
Q

If the nondisjunction occurred in Meiosis 1 what is seen?

A

The two chromosomes from this parent are not identical

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24
Q

What is recombination (cross over)?

A

Mixing up of DNA during meiosis

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25
Q

Where does nondisjunction most commonly occur?

A

Maternally in M1

26
Q

Which nondisjunction is always from the father?

A

47,XYY

Always in meiosis 2

27
Q

How does the risk of Down syndrome increase?

A

With maternal age

35 is the age where testing is recommended

28
Q

What is trisomy 13?

A

Palau syndrome

29
Q

What are the clinical presentations of trisomy 13?

A 
Cleft lip/palate (often severe)
Microcephaly & mental retardation 
Cardiac defects
Genito-urinary and renal defects
Polydactyly
30
Q

How long do babies with trisomy 13 survive?

A

7 days

31
Q

What is the common name for trisomy 18?

A

Edwards syndrome

32
Q

What are the clinical presentation of trisomy 18 (Edwards syndrome)

A 
Microcephaly
CNS and cardiac malformation
Prominent occiput
Micrognathia
Low set ears
Short neck
Overlapping fingers
Renal malformation
Limited hip abduction
Rocker-bottom feet
33
Q

What is the mean survival for Edwards syndrome?

A

14.5 days

34
Q

What is the karyotype for Turner syndrome?

A

45,x

35
Q

What are the clinical presentation of Turner syndrome?

A 
Short stature
Delayed pubertal development
Amenorrhea
Iq ~90
Webbing of neck
Broad chest and infertility 
Infertility
36
Q

What treatment is used for Turner syndrome?

A

Estrogen supplementation

37
Q

Most cases of Turner syndrome are what?

A

45x/46xx mosaics

38
Q

What are the clinical presentation of Klinefelter syndrome (47XXY)?

A 
Secondary sex characteristics display feminization (gynecomastia, female distribution of pubic hair)
Hypogonadism
Infertile due to azospermia 
Disproportionately long limbs
Tall, thin stature
In ~85-90
39
Q

What is the treatment for klinefelters syndrome (47XXY)

A

Testosterone supplementation

40
Q

What is triple x syndrome?

A

47,xxx

Female with tall stature and mild mental deficit

41
Q

What can you see in fluorescentes stained cells of individuals with additional X chromosomes?

A

Barr bodies

Normally only 1 Barr body because 1 X chromosome is inactive. Additional X chromosomes also becomes Barr bodies

42
Q

How do structural chromosomal abnormalities occur?

A

Chromosome breakage with subsequent reunion in a different configuration

43
Q

What s a quadrivalent?

A

When two derived pairs of chromosomes come together during meiosis. When they are pulled in anaphase 6 outcomes are possible (2 balance and 4 unbalanced)

44
Q

What is a roberstsonian translocation?

A

Translocation between 2 acrocentric chromosomes (13,14,15,21,22)
P arms are lost (no essential genetic data)
Q arms nod centromeres are retained as fused chromosomes

45
Q

What is lost in a robertsonian translocation and why is it significant?

A

P arms are lost

No genetic information is carried on the p arm. It s only repetitive rDNA

46
Q

When can Robert translocations occur?

A

When the chromosome is acrocentric

E.g. (21,22,13,14,15)

47
Q

Are carriers of Robert translocations affected? What about their offspring?

A

Carriers are asymptomatic but often produce unbalanced gametes which can result in monosomic or trisomic zygote. ( most wont survive)

48
Q

What are the 6 possible offspring of a 45,xx,rob(14q21q)?

A

2 healthy (1 normal, 1 balance carrier)

3 prenatal lethal (trisomy 14, monosomy 14, monosomy 21)

1 with Down syndrome

-probably of a child being born with Down syndrome is 1/3

49
Q

What is a translocation Down syndrome?

A

An extra copy of the q rm of chromosome 21 due to robertsonian translocation

50
Q

What is the probability that a balanced 14q21 carrier will have a child with Down syndrome?

A

1/3 of live born hypothetically

10% for mother and 3% for father empirically

51
Q

What is the probability that a 21q21q translocation would result in Down syndrome in off spring?

A

100% of live born off spring would have Down syndrome

52
Q

What are the possible gametes for offspring from an individual with 21q21q?

A

Nullisomic for 21: lethal in utero

Disomic for 21: result in trisomic conceptos (Down syndrome child)

53
Q

What are the chromosomal abnormalities if 2 breaks occur in the same arm of the chromosome?

A

Paracentric ( flips around and goes back in)

Interstitial deletion ( it goes bye bye)

54
Q

What happens when there are 2 breaks in different arms?

A

Pericentric inversion ( it flips round )

Ring chromosome ( they reconnected to the other side and lose genetic information at the ends)

55
Q

Which type of inversion involve the centromere?

A

Pericentric inversions

56
Q

What is the critical region in the 4p arm?

A

4p16

57
Q

When does wolf-hirschhorn syndrome occur?

A

When you have a deletion on the 4p arm

It will be abbreviated as 4p-

58
Q

What are the clinical presentations of wolf-hirschhorn syndrome?

A

Face: broad, flat nasal bridge, high forehead (“Greek warrior helmet”)

Microcephaly

Growth retardation

Severe mental deficiency

Hypotonia, seizures

59
Q

When does cri du chat syndrome occur?

A

When there is a deletion in the 5p arm

It is abbreviated as 5p-

60
Q

What are the clinical presentation of cri du chat syndrome?

A

Cat like cry
Mental deficiency
Microcephaly

Face: hypertelorism, epicanthal folds, downward sloping palpebral fissures

Mcb1 (13 decks)

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