Structural Chromosomal Abnormalities

Question 1

Balanced rearrangement

Answer 1

Individuals with balanced rearrangements have normal complements of chromosomal material, meaning there is no loss of genetic material. However, these rearrangements have varying stabilities during meiosis and mitosis.

Question 2

Inversion

Answer 2

occurs when one chromosome undergoes two double strand breaks of the DNA backbone and the intervening sequence is inverted prior to the rejoining of the broken ends

Question 3

Paracentric inversions ________ the centromere

Answer 3

exclude

Question 4

Pericentric inversions ________ the centromere

Answer 4

include

Question 5

Reciprocal translocation

Answer 5

results from the breakage and rejoining of non-homologous chromosomes, with a reciprocal exchange of the broken segments

Question 6

Alternate segregation produces

Answer 6

gametes that have either the normal chromosome complement or two reciprocal translocation chromosomes, both of which are balanced with respect to chromosome complement

Question 7

Robertsonian translocation

Answer 7

the fusion of two acrocentric chromosomes within their centromeric regions, resulting in the loss of both short arms (containing rDNA repeats)

Question 8

Unbalanced rearrangement

Answer 8

the chromosome set has additional or missing material. Phenotypes of these individuals are likely to be abnormal. Duplication of genetic material in gametes can lead to partial trisomy after fertilization with a normal gamete, while deletions lead to partial monosomy

Question 9

Deletion

Answer 9

loss of genetic information that can arise by simple chromosome breakage and rejoining, unequal crossing over between misaligned homologous chromosomes or sister chromatids, or by abnormal segregation of a balanced translocation or inversion

Question 10

Chromosomal rearrangements require ________ and can be induced by ________

Answer 10

two DNA double strand breaks (DSBs)

a variety of DNA damaging agents

Question 11

disease associated with reciprocal translocation

Answer 11

chronic myelogenous leukemia

Question 12

disease associated with a deletion

Answer 12

Cri-du-chat syndrome

Question 13

duplication

Answer 13

gain of genetic information, which is generally less harmful than deletion, but can lead to abnormalities (i.e. partial trisomy 21).

Question 14

Ring Chromosome

Answer 14

a chromosome fragment that circularizes and acquires kinetochore activity for stable transmission to daughter cells (also called a marker chromosome)

Question 15

Isochromosome

Answer 15

a chromosome in which one arm is missing and the other duplicated in a mirror-image fashion, possibly occurring through an exchange involving one arm of a chromosome and its homolog at the proximal edge of the arm, adjacent to the centromere

Question 16

A small percentage of Down syndrome patients have the 21q21q ________

Answer 16

isochromosome

Question 17

Most chromosome structural abnormalities found in fetuses and newborns that are associated with serious clinical effects are attributable to ________

Answer 17

a random event

Question 18

Occasionally a serious chromosomal abnormality can be inherited from a seemingly normal parent who carries a ________ such as a translocation. In these comparatively rare cases, the recurrence risk could be much ________

Answer 18

balanced chromosomal abnormality

increased

Question 19

Contiguous gene syndromes

Answer 19

abnormal phenotypes caused by over-expression or loss (haploinsufficiency) of neighboring genes

Question 20

Wolf-Hirschhorn syndrome

Answer 20

• deletion

- facial clefting, prominent ears, microcephaly, intellectual disabilities

Question 21

Beckwith-Wiedemann syndrome

Answer 21

• duplication
• paternal
• overgrowth, omphalocele, predisposition to Wilms, other tumors

Question 22

Cri du chat syndrome

Answer 22

• deletion

- microcephaly, characteristic cry, seizures, intellectual disabilities

Question 23

Angelman syndrome

Answer 23

• deletion
• maternal
• seizures, intellectual disabilities

Question 24

Williams syndrome

Answer 24

• deletion

- congenital heart disease, short stature

Question 25

Prader-Willi syndrome

Answer 25

• deletion
• paternal
• hypotonia, hypopigmentation, hypogenitalism, obesity

Question 26

Langer-Giedion syndrome

Answer 26

• deletion

- Tricho-rhino-pharangeal syndrome, multiple exostoses

Question 27

Miller-Dieker syndrome

Answer 27

• deletion

- lissencephaly (agyria), profound intellectual disabilities

Question 28

WAGR syndrome

Answer 28

• deletion

- Wilms tumor, aniridia, genitourinary anomalies, intellectual disabilities

Question 29

DiGeorge syndrome

Answer 29

• deletion
• absent or hypoplastic thymus and parathyroids, congenital heart disease, Velo-Cardio-Facial syndrome, cleft palate, lateral nasal buildup, cardiac septal defects