Cytogenetics and Chromosomal Disorders

Question 1

During meiosis I homologous chromosomes or segments will pair with each other.
Karyotype: 46,XY,t(3;11)(q13;p14)
How many chromosomal pairing units would you expect to find?

Answer 1

22
(21 normal units and 1 quadrivariant)

Question 2

What are hte possible reproductive outcomes for 46,XY,t(3;11)(q13;p14) with a normal partner?

Answer 2

Normal (clinically and karyotypically)
Translocation carrier
Spontaneous abortion/stillbith
Live-born with congenital defect
AKA
6 outcomes:
1 normal
1 balanced carrier
4 unbalanced

I guess he is saying that the partial monosomies/trisomies are often not viable with life or result in congenital defects

Question 3

translocation carriers + normal partner = homany chromosomal compositions for the fetus?
Ex: 46,XX,t(1;3)

Answer 3

6
This is becuase of meiotic quadrivalent segregation.

Question 4

Describe 46,XX,r(8)(p13q22)

Answer 4

A female with a ring 8 chromosome and is consequently partially monosomic for 8p and 8q

Question 5

Does pericentric or paracentric invrsion lead to acentric and dicentric chromosomes?

Answer 5

paracentric
acentric and dicentric chromosomes cause gamete loss or early embryonic loss so are not compatible with life. This is why pericentric inversions are associated with birth defects, but paracentric inversions are not.

Question 6

Which of hte following findings is the greatest risk factor for someone to have a liveborn child with multiple malformations?
A. Being 30 years old
B. being 46,XX/45,X
C. large paracentric inversion of chromosome 2
D. large pericentric inversion of chromosome 2
E. brother with 47,XY,+21

Answer 6

D. large pericentric inversion of chromosome 2

pericentric inversions are not as severe as paracentric inversion, so are compatible with life, but lead to affected offspring.

Question 7

Which one of the following chromosomal abnormalities results in the smallest decrease in reproductive fitness?
A. Triploidy
B. Trisomy 13
C. Klinfelter syndrome
D. Turner syndrome
E. Pericentric inversion

Answer 7

E. Pericentric inversion
Turner syndrome: high risk for POI & infertility
Klinefeltersyndrome: produce little to no sperm

Question 8

Which type of chromosomal change has a very low likelihood of resulting in a liveborn child with a chromosomal abnormality?

Answer 8

paracentric inversion

becuase children are either chromosomally normal or incompatible with life

Question 9

Which one of the following cytogenic abnormalities found in a first trimester fetus results in the highest rate of spontaneous fetal loss?
A. 45,X
B. 47,XX,+18
C. 47,XX,+21
D. 47,XXX
E. 47,XXY

Answer 9

A. 45,X

Question 10

A man is found to have 45 chromosomes becuase his two chromosome 21s are joined at the centromere to form a single chromosome (i.e. 21/21 Robertsonian translocation).
Which one of the following statements is true concerning his gametes?
A. He has 23 chromosomes in each of his sperm.
B. He has 22 chromosomes in each of his sperm.
C. He has a mixture of sperms, some of which has 22 chromosomes and some have 23 chromosomes.
D. He has 45 chromosomes in each of his sperm.

Answer 10

C. He has a mixture of sperms, some of which has 22 chromosomes and some have 23 chromosomes.

Question 11

A man is found to have 45 chromosomes becuase his two chromosome 21s are joined at the centromere to form a single chromosome (i.e. 21/21 Robertsonian translocation).
The likelihood of each of his children to have Down syndrome is:
A. 1%
B. 25%
C. 50%
D. 100%

Answer 11

D. 100%