Structural Rearrangements

Question 1

Percent of structural abnormalities in patients with ID or autism

Answer 1

15-20%

Question 2

Incidence of structural abnormalities (livebirths and conceptions)

Answer 2

1:400 livebirths, 1:200 conceptions

Question 3

Structural abnormalities more likely to occur in maternal or paternal meiosis

Answer 3

paternal

Question 4

Interstitial deletions percent

Answer 4

84% paternal

Question 5

Terminal deletions percent

Answer 5

70% paternal

Question 6

Duplications percent

Answer 6

58% paternal

Question 7

Translocations percent

Answer 7

62% paternal

Question 8

Reciprocal translocations percent

Answer 8

96% paternal

Question 9

Robertsonian translocations are mostly maternal or paternal in origin

Answer 9

maternal

Question 10

Recurrence risk for numerical abnormalities

Answer 10

1% in mid 30s

Question 11

Recurrence risk for structural abnormalities

Answer 11

1-50%

Question 12

Incidence of robertsonian translocation

Answer 12

1:1,000

Question 13

Acrocentric chromosomes

Answer 13

13, 14, 15, 21, 22

Question 14

Most common robertsonian translocation and percent

Answer 14

13;14 75-85%

Question 15

Second most common type of robertsonian translocation and percent

Answer 15

14:21 8-10%

Question 16

least common type of robertsonian translocation and what type of inheritance event

Answer 16

homologous and de novo

Question 17

21;21 rob translocation is what risk

Answer 17

100%

Question 18

Reciprocal translocation incidence

Answer 18

1:700-1:1000

Question 19

Reciprocal translocation

Answer 19

exchange of genetic material between non-homologous chromosomes or at non-homologous sites

Question 20

Percent of balanced reciprocal translocations that are inherited

Answer 20

70%

Question 21

If reciprocal translocation is inherited, what is the risk

Answer 21

no increased risk

Question 22

If reciprocal translocation is de novo, risk is

Answer 22

6-7%

Question 23

Percent of reciprocal translocations that are de novo

Answer 23

30%

Question 24

small distal segments lead to

Answer 24

small imbalances and large risks for clinically affected live born children

Question 25

Large distal segments lead to

Answer 25

large imbalances and low risks for having live born abnormal children (high risks for miscarriages and period of infertility)

Question 26

Partial trisomies compatiable with life

Answer 26

8, 9, 13, 18, 21, x, y

Question 27

Partial monosomies that are compatible with life

Answer 27

4p, 5p, x, y

Question 28

Empiric risk of unbalanced liveborn child with previous child with unbalance

Answer 28

20-25%

Question 29

Empiric risk of unbalanced liveborn child with multiple miscarriages and no liveborn unbalanced individuals

Answer 29

2-4%

Question 30

Empiric risk of unbalanced liveborn child who was accidentally ascertained (ex: through amnio)

Answer 30

4-5%

Question 31

Factors that help drive reproductive risk for translocation

Answer 31

mode of ascertainment, size of exchanged segment, and chromosome regions involved

Question 32

Inversions

Answer 32

two-break intrachromosomal rearrangement in which material flips over or reverses orientation

Question 33

Percent of inversions that are inherited

Answer 33

80-90%

Question 34

Pericentric inversions

Answer 34

centromere is included between the two breakpoints

Question 35

Paracentric inversion

Answer 35

centromere is not between two breakpoints

Question 36

Duplication-deficiency recombinant chromosomes

Answer 36

odd number of crossovers that leads to loss of material

Question 37

Normal recombinant chromosomes

Answer 37

even number of crossovers, no net gain or loss of material

Question 38

The larger the inversion

Answer 38

higher risk for live born abnormal child - have small distal segments, which produce small imbalances - farther apart the breakpoints, the more likely crossovers will occur between them and form recombinant duplication/deficiency chromosomes

Question 39

Small inversions

Answer 39

less likely to be associated with live born abnormal child

Question 40

Empiric risk of pericentric inversion through abnormal child

Answer 40

5-15%

Question 41

Empiric risk of pericentric inversion if ascertained fortuitously through prenatal diagnosis

Answer 41

1%

Question 42

Types of chromosomes formed from paracentric inversions

Answer 42

dicentric and acentric

Question 43

Empiric risk of unbalanced offspring with paracentric inversion is

Answer 43

.1-.5%

Question 44

Insertions

Answer 44

3 break rearrangements where a piece of chromosomal material is excised from one location and inserted at a new location

Question 45

Incidence of insertions

Answer 45

1:80,000-1:10,000

Question 46

Intrachromosomal insertions

Answer 46

all 3 breaks within the same chromosome

Question 47

Interchromsomal insertions

Answer 47

break points in different chromosomes

Question 48

Empiric risk of intrachromosomal insertion in abnormal child

Answer 48

50%

Question 49

Empiric risk of interchromosomal insertion abnormal child

Answer 49

32-36%

Question 50

Ring chromosome

Answer 50

when a chromosome undergoes 2 breaks and the broken ends reunite in ring structure

Question 51

result from a ring chromosome that replaces normal chromosome

Answer 51

partial monosomy

Question 52

Result of a supernumerary ring chromosome

Answer 52

partial trisomy

Question 53

How are ring chromosome usually passed down

Answer 53

de novo

Question 54

incidence of ring chromosomes

Answer 54

1:27,225

Question 55

Most common ring chromosomes

Answer 55

13 and 18

Question 56

Typical phenotype of ring syndrome

Answer 56

severe growth restriction without major malformations, mild-moderate ID, minor anomalies

Question 57

Ring chromosomes are _________ during mitosis

Answer 57

unstable

Question 58

Dynamic mosaicism seen more commonly in what kind of rings

Answer 58

larger

Question 59

Percent of non-supernumerary rings that are inherited and by who

Answer 59

1% and mother

Question 60

Empiric risk of transmission of ring chromosome

Answer 60

40%

Question 61

Number of ring chromosome cases with severe phenotype

Answer 61

1:3

Question 62

Probability that parent is balanced carrier when child is balanced carrier Trisomy 21

Answer 62

50-60%

Question 63

Reproductive risk for balanced carriers of Trisomy 21

Answer 63

unbalanced offspring, miscarriages, UPD

Question 64

How do balanced translocation chromosomes pair during meiosis and types

Answer 64

quadrivalent formation in meiosis, alternate, adjacent 1, adjacent 2

Question 65

alternate 2:2 segregation forms

Answer 65

balanced offspring

Question 66

adjacent 1 segregation

Answer 66

second most likely type of segregation

Question 67

Adjacent 2 segregation is typically

Answer 67

lethal

Question 68

Inverted homologues form

Answer 68

inversion loops during meiosis I

Question 69

Offspring of parents who have recombinant imbalanced chromosomes are more likely to inherit what type of structural rearrangement

Answer 69

a balanced inversion

Question 70

Which of the following statements are true about rings

Answer 70

Rings are responsible for dynamic mosaicism which can cause variation in skin pigmentation and growth reduction.

Question 71

A mother with a 46, XX karyotype and a father with a 45, XY, rob(14;21)(q10;10) karyotype plan to have a child together. They are worried about having a child with Down Syndrome. Which of the following gametes produced from the father would the child not have Trisomy 21 but still be a carrier for a Robertsonian translocation after fertilization, given that the mother gives a gamete with an independent chromosome 14 and an independent chromosome 21

Answer 71

A gamete with a derivative 14, 21 chromosome only

Question 72

Which of the following situations could not produce a gamete that could lead to a child with a partial or full trisomy

Answer 72

anaphase lag