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M2M Genetics > Structural Chromosomal Abnormalities > Flashcards

Structural Chromosomal Abnormalities Flashcards

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1
Q

what is the cause of chromosomal rearrangements?

A

double stranded DNA breaks

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2
Q

when are DNA double stranded breaks normal?

A

during recombination

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3
Q

where do DNA double strand breaks occur the most?

A

regions in chromosomes where repeated sequences are prevalent

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4
Q

what are the 5 rearrangements of chromosomes?

A
  1. deletion
  2. insertion
  3. inversion
  4. translocation
  5. duplication
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5
Q

what are the 3 types of balanced rearrangements?

A
  1. inversions
  2. reciprocal translocation
  3. robertsonian translocation
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6
Q

what is considered a balanced structural rearrangement?

A

normal complement of chromosome material (no loss of genetic material)

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7
Q

what is an inversion?

A

two double strand breaks, intervening sequence is inverted and the broken ends are rejoined

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8
Q

what is a paracentric inversion?

A

an inversion that excludes the centromere

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9
Q

what is a pericentric inversion?

A

an inversion that includes the centromere

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10
Q

what can occur if recombination occurs with a paracentric inversion chromosome?

A

dicentric chromosomes (two centromeres) and acentric chromosomes (no centromere) can be formed which can lead to breakage or loss

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11
Q

what can occur if recombination occurs with a pericentric inversion chromosome?

A

duplications and deletions

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12
Q

with inverted chromosomes, what is a likely structure that will form to facilitate recombination?

A

a loop to match up homologs

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13
Q

what is a reciprocal translocation?

A

breaking and rejoining of non-homologous chromosomes, with a reciprocal exchange of the broken segments

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14
Q

where are balanced translocations usually found?

A

in couples that have had 2 or more spontaneous abortions, also in infertile males

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15
Q

what is formed when reciprocal translocations come together prior to segregation during meiosis?

A

quadrivalent figure

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16
Q

what are the 3 ways that the quadrivalent figure can be segregated?

A
  1. alternate
  2. adjacent-1
  3. adjacent-2
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17
Q

what does the alternate segregation pattern of reciprocal translocations form?

A

normal or balanced gametes

normal chromosome complement or 2 reciprocal translocation chromosomes

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18
Q

what is the most common segregation of reciprocal translocations?

A

alternate segregation

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19
Q

what does the adjacent-1 segregation of reciprocal translocations form?

A

unbalanced gametes

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20
Q

what does the adjacent-2 segregation of reciprocal translocations form?

A

unbalanced gametes

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21
Q

what is the lethality of reciprocal translocations?

A

5-10%

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22
Q

what does a translocation between chromosome 9 and 22 usually result in?
46, XX t(9;22)(q32;q11.2)

A

chronic myelogenous leukemia

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23
Q

what does this karyotype mean?

46, XX inv(9) (p13q13)

A

female with inversion of sequences between band 13 on short arm and band 3 on long arm of chromosome 9

24
Q

what is a robertsonian translocation?

A

fusion of two acrocentric chromosomes within centromeric regions resulting in loss of both short arms

25
Q

what do short arms of acrocentric chromosomes usually contain

A

rDNA repeats

26
Q

what is the most common chromosome rearragement in our species?

A

translocation of 13q and 14q

1 in 1300 people

27
Q

what is the most important clinical aspect of robertsonian translocations?

A

robertsonian translocation involving chromosome 21 can lead to translocation down syndrome

28
Q

what happens to the karyotype of a robertsonian translocation?

A

reduction in number of chromosomes (most commonly to 45 but sometimes to 44

29
Q

True or False

Robertsonian translocations are considered unbalanced rearrangements and lead to abnormal phenotypes

A

False

Robertsonian translocations are considered BALANCED and lead to NORMAL phenotypes

30
Q

what happens to the offspring of robertsonian translocation patients?

A

unbalanced karyotypes resulting in monosomies and trisomies

31
Q

what are 2 common robertsonian translocations?

A

13q and 14q

14q and 21q

32
Q

how is a robertsonian translocation abbreviated?

A

“der” or “rob”

33
Q

what is an unbalanced structural rearrangement?

A

chromosome has additional or deleted material and is unbalanced leading to abnormal phenotype

34
Q

what are the 4 types of unbalanced structural arrangements?

A
  1. deletion
  2. duplication
  3. ring chromosome
  4. isochromosome
35
Q

what are the 2 types of deletions?

A
  1. terminal (at end)

2. interstitial (on inside)

36
Q

what is the clinical consequence of deletions?

A

haploinsufficiency

37
Q

what is haploinsufficiency?

A

contributions of the remaining gene is not enough to prevent disease or express the normal phenotype

38
Q

what determines the severity of a phenotype in a deletion?

A

the size of the deletion and the number of genes affected

39
Q

what is the abbreviation used to express a deletion?

A

del

40
Q

what does this karyotype mean?

46, XY del (5)(p15)

A

male with deletion on short arm at one-five on the 5th chromosome
results in Cri-du-chat syndrome

41
Q

what is a duplication?

A

gain of genetic material, less harmful than deletion

42
Q

what is a partial trisomy a result of?

A

duplication

43
Q

what are the 2 ways that duplications can occur?

A
  1. unequal crossing over

2. abnormal segregation in meiosis

44
Q

what is a ring chromosome?

A

centromere joins itself and gain kinetochore activity

45
Q

what is another name for a ring chromosome?

A

marker chromosome

46
Q

how is a ring chromosome abbreviated?

A

r

47
Q

what is an isochromosome?

A

chromosome that has a missing arm and the other arm is duplicated in a mirror image fashion

48
Q

how is an isochromosome abbreviated?

A

i

49
Q

what is the most common isochromosome observed?

A

long arm of X chromosome i(Xq)

50
Q

how can an isochrome cause down syndrome?

A

there is an isochromosome with 21q21q and then there is a normal 21 chromosome. This is 3 21 chromosomes which leads to DS

51
Q

what disease would this karyotype lead to?

46, XX (21) (21q21q)

A

Down syndrome

52
Q

in general, what is the chance of recurrence with a family that had a baby with abnormal karyotype?

A

very low, chromosomal structural abnormalities are very rare and due to a random event, unlikely to occur again. plus if one occurred, recurrence could be diagnosed during utero of the next baby

53
Q

what is a contiguous gene syndrome?

A

abnormal phenotypes caused by over-expression or loss of neighboring gene

54
Q

what are the 2 contiguous gene syndromes that occur from deletions on the long arm of chromosome 22?

A

velocardiofacial syndrome

digeorge syndrome

55
Q

what is the phenotype of velocardiofacial syndrom?

A

cleft palate

septal defects

56
Q

what is the phenotype of digeorge syndrome?

A

neural crest, branchial pouches, great vessels

outflow tract defects in the heart

57
Q

what do most chromosomal disorders result in?

A

miscarriage

M2M Genetics (10 decks)

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