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Term I: Genetics > Cytogenetics > Flashcards

Flashcards in Cytogenetics Deck (31)
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1
Q

What letters represent the short and long arms of a chromosome?

A

Short arm: p, Long arm: q

2
Q

What is a metacentric chromosome?

A

The short and long arm are equal in size

3
Q

What is a sub-metacentric chromosome?

A

The short and long arm are unequal in size.

4
Q

What is an acrocentric chromosome?

A

The short arm is very small and close to the centromere.

5
Q

What is the most common technique that is used for blood karyotyping? Describe the process.

A

G-bandin - Lymphocytes (T-cells) from peripheral blood are stimulated with phyohemaglutinin (PHA) and cultured for 72 hours before being placed in a hypotonic solution (KCl) to arrest division. Cells are then fixed on slides with methanol/acetic acid. Banding is achieved by trypsin treatment for G-bands and staining with Giemsa. Results in GC rich light bands and AT rich dark bands

6
Q

What do del, dup, mar, stand for?

A

Deletion, duplication, marker

7
Q

Describe what the karyotype 46,XY,del(5)(p15.2) indicates.

A

Male with normal number of chromosomes who has a deletion of part of the short arm of one of his chromosome #5s.

8
Q

What karyotype does a Turner syndrome patient have?

A

45,X (females) - this is a monosomy X

9
Q

What karyotype does a Klinefelter syndrome patient have?

A

47, XXY (males)

10
Q

What karyotype does a female with trisomy 21 (Down syndrome) have?

A

47,XX,+21

11
Q

What is euploidy?

A

Normal, balanced set of chromosomes

12
Q

What is diploidy?

A

Normal number of chromosomes in a somatic cell (2n)

13
Q

What is haploid?

A

Chromosome number of gametes in mature egg or sperm (1n so it can be 23,X or 23, Y in humans)

14
Q

What is aneuploidy?

A

Unbalanced number of chromosomes, where either one is missing or you have an additional chromosome (2n-1 or 2n+1) Ex: trisomy 21

15
Q

What is triploidy? What are the three ways it can occur?

A

3 haploid sets (3n)

1) Dispermy - ovum is fertilized by two sperm to yield a triploid zygote (most common cause)
2) Fertilization by diploid sperm
3) Non-disjunction in the egg

16
Q

What is polyploidy?

A

Having extra sets of chromosomes
Ex: triploidy: 68,XXX or 69,XXY

tetraploidy: 96,XXXX
mixoploidy: 46,XX/69,XXX

17
Q

What are the two potential consequences of triploidy?

A

1) 2 maternal + 1 paternal = normal fetal development, small placenta
2) 2 paternal + 1 maternal = abnormal fetal growth, increased placental development

18
Q

What is nondisjunction?

A

The aberrant segregation of homologous chromosomes into the same daughter cell - occurs most often in Meiosis I of oogenesis and is associated w/ advanced maternal age

19
Q

What is mosaicism? What are the two different types?

A

Mixture of two or more cell lines in an individual (Ex: 45,X/46,XX) May result from error in disjoining of chromatids in mitosis

Constitutional mosaicism - numerical chromosome abnormalities

Gonadal mosaicism - involves testes and ovaries

20
Q

Describe what yellow, red, and green mean in a Comparative Genomic Hybridization Array (aCGH)/chromosome microarray.

A

Red - patient has less DNA than the control (deletion)

Green - patient has more DNA than the control (duplication)

Yellow - DNA is equal in patient and control

21
Q

Describe what the 0 line is in the Array profile and what marks in the negative and positive direction indicate.

A

0 line = normal

Left of 0 line/negative = deletions

Right of 0 line/positive = duplication

22
Q

What are some of the limits of microarray methodology?

A

Cannot detect balanced rearrangements, does not provide information regarding location of additional copy, copy number variations may or may not be pathogenic

23
Q

What is fluorescence in situ hybridization (FISH)?

A

Complementary stretch of DNA (probe) is labeled and hybridized onto a cell. FISH can then identify specific chromosomal regions that have been deleted or duplicated - location specific. It is used clinically as a confirmation for diagnoses from microarray studies.

24
Q

What are the two types of chromosomal deletions? And given an example of each.

A

Terminal - at ends of chromosomes (Wolf-Hirschorn Syndrome, deletion on chromosome 4)

Interstitial - in middle of chromosomes (Smith-Magenis syndrome, deletion on chromosome 17)

25
Q

What is a chromosomal duplication and what are the two different types?

A

Duplication is when a visible chromosomal segment is present twice on the same chromosome.

Direct, Inversion

26
Q

What is Williams Beuren Syndrome? What happens when a duplication occurs in this same chromosomal region?

A

Interstitial microdeletion of chromosome 7 - CV disease, distinctive face, overfriendliness, ADD

If duplication occurs in same chromosomal region, result is autism

27
Q

What are the two types of inversion duplication?

A

Pericentric - 2 breaks on either side of centromere - results in duplication deficiency chromosomes

Paracentric - 2 breaks on same chromosome arm, not involving centrome - results in acentric and dicentric chromosomes

28
Q

What are ring chromosomes?

A

Deletion of terminal short arm and terminal long arm results in the unstable ends rejoining

29
Q

What is a translocation?

A

Exchange or transfer of chromosomal segments between two ore more chromosomes.

30
Q

What is a Robertsonian translocation?

A

Originates through joining of long arms of acrocentric (centromere is at end of chromosome instead of the middle) chromosomes 13,14,15,21, and 22

31
Q

What will be the recurrence rate for a woman with monosomic 21?

A

100% recurrence - Monosomy means she only has one chromosome 21, so all of her children will have trisomy 21 (Down’s syndrome) b/c her 21 is not viable