Sollars - Chromosome Abnormalities

Question 1

Aneuploid

Answer 1

Addition or Loss of Chromosomes

Question 2

Monosomic

Answer 2

2n - 1

Question 3

Trisomic? Major conditions (e.g. survivable)

Answer 3

2n + 1 13/18/21/X/Y

Question 4

What is the source for most polyploidies?

Answer 4

Nondisjunction in Meiosis 1 or Meiosis 2

Question 5

What is the process for nondisjunction in mitosis?

Answer 5

Sister chromatids fail to migrat to opposite poles during anaphase; can result in mosaicism

Question 6

Trisomy 21 Mosaicism

Answer 6

If nondisjunction occurs after the first division, but early in zygote development

Question 7

Trisomy 13

Answer 7

Patau 1/25,000 Cleft lip, extra digits, ocular abnormalities; usually lethal by 6 mon

Question 8

Trisomy 18

Answer 8

Edwards (Eighteen = Edwards, E’s) 1/8,000; 95% spon aborted 80% Female, elf ears, clenched firsts, rocker-bottom feet; usually lethal by 6 mon

Question 9

Trisomy 21

Answer 9

Downs Most common trisomy Mental retardation, palmer crease, specific eye and facial features; majority cause is maternal non-disjunction; increases with mother age

Question 10

Tris 13/18 account for what percentage of spon abortions?

Answer 10

95

Question 11

What is one of the few main autosomal monosomies?

Answer 11

Turner Syndrom (Xo)

Question 12

What is the translocation that occurs in “hereditary” downs?

Answer 12

14q21q

Question 13

What is the main source of DS?

Answer 13

75-50% = M1 nondisjunction in mother M2 account for remainder

Question 14

Hereditary/Familial Aneuploidy

Answer 14

More rare; mutation present in all germline and somatic cells

Question 15

1^o Non Disjunction

2^o Non Disjunction

Answer 15

Primary - Nondisjunction occuring in cells with normal chromosome number

Secondary - Nondisjunction occurs at higher frequency in aneuploid cells

Question 16

General frequency of chromomal abnormalities

Answer 16

~.6% of live births in general population

Of this, half are trsiomies, half are structural

Question 17

Rough Percentage of Maternal vs Paternal contribution for:

Trisonomies

45,X

47,XXX

47,XXY

47,XYY

Answer 17

Trisonomies: P = 15, M = 85

45, X: P = 80

47, XXX: M=95

47,XXY: 50/50

47,XYY: P=100

Question 18

How would you determine parental risk for Robertsonian translocation?

Answer 18

Karyotyping

Question 19

What region of 21 has been identified as a likely candidate for mental retardation phenotype?

Answer 19

q22.3

Question 20

Contiguous Gene Syndrome

Answer 20

Deletion of a segment of DNA containing portions from multiple adjacent genes – e.g:

Loss of function of multiple genes next to eachother