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1

What is clinical cytogenetics?

The study of abnormalities of chromosome number and structure in relation to human disease

2

True or false - cytogenetic abnormalities are collectively more common than all Mendelian single gene disorders.

True

3

Cytogenetic abnormalities account for ___ live births.

1/154

4

The incidence of cytogenetic abnormalities in children of mothers >35 years old is ___.

1/50

5

What are the 6 major indications for cytogenetic analysis?

1. Problems with early childhood growth and development (failure to thrive, abnormal physical appearance and/or internal structural abnormalities, mental retardation, ambiguous genitalia)
2. Stillbirths and neonatal deaths that have the appearance of a cytogenetic abnormality
3. History of infertility or recurrent miscarriage
4. Known or suspected chromosome abnormality in a first degree relative
5. Maternal age >35
6. Cancer

6

What are the common types of dividing nucleated cells or tissues used for cytogenetic analysis?

1. White blood cells (T lymphocytes) from peripheral blood
2. Amniotic cells
3. Cell of the chorionic villi (extra-embryonic fetal tissue that form the surface of the chorionic sac)
4. Fibroblasts
5. Cancer cells
6. Bone marrow

7

How are chromosomes classified?

By position of centromere

8

What are the 3 classifications of chromosomes?

1. Metacentric: centromere found midway
2. Submetacentric: centromere off-center, arms of equal length
3. Acrocentric: centromere very near on end, produces p arm known as a satellite

9

What are the 5 acrocentric chromosomes in humans?

13, 14, 15, 21, 22

10

Acrocentric satellite arms contain many copies of genes coding for ___.

rRNA

11

___ created by various staining procedures are unique to each chromosome.

Banding patterns

12

Which chromosome arm is longer? Which is shorter?

q; p

13

How are chromosomes numbered?

Example: 1p12 = chromosome 1, p arm, region 1, band 2 - note that regions are numbered from the centromere to the telomere

14

Normally, staining occurs during ___. However, higher resolutions are obtained when chromosomes are less condensed and are in ___.

Metaphase; prophase or prometaphase

15

What are the properties of dark bands stained with Giemsa?

1. Stains strongly with quinicrine
2. Maybe AT-rich
3. Early condensation, late replication
4. Gene poor
5. Alu poor, LINE rich

16

What are the properties of pale bands stained with Giemsa?

1. Stains weakly with quinicrine
2. Maybe CG-rich
3. Late condensation, early replication
4. Gene rich
5. LINE poor, Alu rich

17

What are several alternative chromosome staining methods?

1. Q-banding (uses quinicrine, correlates to G-bands)
2. R-banding (reverse Giemsa pattern)
3. Fluorescence R-banding (fluorescent bands correlate to light bands in Giemsa)
4. Prometaphase banding (higher resolution, G or R-banding)

18

What do the following abbreviations stand for regarding the description of chromosomal abnormalities?
1. ,
2. -
3. ( )
4. +
5. ;
6. del
7. der
8. dic
9. dup
10. fra
11. i
12. ins
13. inv
14. .ish
15. mar
16. mat
17. p
18. pat
19. q
20. r
21. rob
22. t
23. ter

1. separates chromosome number, sex chromosome, chromosomal abnormalities
2. loss of chromosome
3. surround structurally altered chromosomes/break points
4. gain of chromosome
5. separates rearranged chromosomes and breakpoints involve more than one chromosome
6. deletion
7. derivative chromosome (translation chromosome derived from 1 chromosome and containing its centromere)
8. dicentric chromsome
9. duplication of a portion
10. fragile site
11. isochromosome (arms are the same)
12. insertion
13. inversion
14. precedes karyotype results from FISH
15. marker chromosome (unidentifiable piece)
16. maternally derived chromosome rearrangement
17. short arm
18. paternally derived chromosome rearrangement
19. long arm
20. ring chromosome
21. Robertsonian translocation
22. translocation
23. terminal end of arm

19

What are aneuploidies?

Abnormalities of chromosome number; most common type of human chromosome disorder

20

What is the frequency of aneuploidies in all pregnancies?

5%

21

___ are incompatible with live births.

Autosomal monosomies

22

Only 3 autosomal trisomies are capable of producing a live birth. What are they, what syndrome do they produce, and what is the frequency?

1. Trisomy 13 (Patau syndrome) - 1/22,700 live births
2. Trisomy 18 (Edward syndrome) - 1/7,500 live births
3. Trisomy 21 (Down syndrome) - 1/580 live births

23

Why can trisomies 13, 18, and 21 still result in a live birth?

These three chromosomes contain the smallest number of genes.

24

True or false - most common sex chromosomal aneuploidies are incompatible with life.

False - most are compatible with life

25

What are two female aneuploidies?

1. Turner Syndrome, monosomy X (45, X), 1/4000 female births
2. Trisomy X (47, XXX), 1/900 female births

26

What is the frequency of all X chromosome aneuploidies?

1/580 female births

27

What are two male aneuploidies?

1. Klinefelter syndrome (47, XXY, 48 XXXY), 1/1000 male births
2. 47, XXY syndrome - 1/1,000 male births

28

What is the frequency of all X or Y aneuploidies?

1/360 male births

29

Aneuploidy is commonly caused by meiotic nondisjunction. What is this?

The failure of chromosomes to detach from each other during one of the two meiotic divisions.

30

What is the result of meiotic nondisjunction in meiosis I? In meiosis II?

I: produces gametes with 1 maternal copy and 1 paternal copy of the extra chromosome.
II: produces a gamete with either 2 maternal or 2 paternal copies of the extra chromosome.