Cytogenetic analysis Flashcards Preview

Human reproduction and fertility > Cytogenetic analysis > Flashcards

Flashcards in Cytogenetic analysis Deck (38)
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1
Q

what groups are metacentric chromosomes?

A

centromere in the middle of the chromosome, group H large metacentrics, group F small

2
Q

what are acrocentric chromosomes?

A

centromere at end of chromosome. group D and G

3
Q

what are submetacentric chromosomes?

A

centromere neither at end or middle

4
Q

in g-banding, where cell cycle are the cells arrested?

A

in metaphase of mitosis

5
Q

what does killing cells with fixative do?

A

blocks chromosome condensation and renders sample inert

6
Q

what bands does the trypsin digest create?

A

pale bands

7
Q

what do you stain it with after trypsin digest?

A

Leishmans dye

8
Q

what sequences are dark and light bands rich in?

A

dark= AT rich. light= GC rich

9
Q

what is open chromatin associated with?

A

darker bands

10
Q

why may the banding structure differ between 2 homologues?

A

due to stage of cell cycle that cell was in when fixative was added, tissue type

11
Q

what can make your chromosomes longer?

A

more mature cells

12
Q

what does a longer trypsin incubation cause?

A

a paler band as chromosome more collapsed so Leichmans cant get into collapsed chromosome

13
Q

what else can influence banding resolution?

A

slide aging, staining time and chromosome spread

14
Q

difference between direct and indirect FISH

A

indirect is when the flourscent dies are added after sample and probes hybridised. more sesitive but slower. direct is much quicker but less sensitive so longer probes required

15
Q

what is DAPI?

A

intercalating agent and used as counter stain

16
Q

how is FISH carried out?

A

heat metaphase spread sample to 75-78 degrees to make DNA ss but not destroy the chromatin structures. then wash to remove unbound probes

17
Q

what is chromosome enumeration dues for detecting?

A

common aneuploidies

18
Q

how is chromosome enumeration carried out?

A

probes made that are specific to certain alpha satellite sequences of common aneuplodies.

19
Q

what does a bright signal allow?

A

allowing rapid hybridisation times and less ambiguity

20
Q

what are microdeletion probes used for?

A

used to check an abnormality detected by G-banding eg Cri du chat. used for detection of small translocation, inversion, deletion, insertion, duplication in parent chromosome which causes unbalanced foetal karyotype

21
Q

what is whole chromosome painting used for?

A

if unsure of origin of fragment of DNA or if dont know where breakpoint is

22
Q

how does dTTP excess arrest cell cycle?

A

inhbits ribonuclease reductase enzyme at high concentration, reduces dCTP conc and becomes rate limiting-arrests DNA synthesis so cells remain in S phase

23
Q

how is the thymidine block released?

A

addition of dCTP to bypass the need for ribonucleotide reductase, or by washing and centrifuging and replacing media to dilute out the excess dTTP

24
Q

what happens once the cells are released from the block?

A

they proceed through mitosis in a synchronous manner

25
Q

what other chemical can be an S phase block?

A

FdU- blocks dTMP synthesis so dTTP conc becomes rate limiting

26
Q

what enzyme breaks down sister chromatid cohesion?

A

separase

27
Q

what does colcemid do to the alpha and beta hetrodimer tubules?

A

destabilises the polymerisation and stops the microtubules from forming

28
Q

what does colcemid block the cell cycle in?

A

metaphase since spindles not formed

29
Q

what is an accurate test?

A

the test detects the genetic condition you are looking for correctly

30
Q

what is a precise test?

A

the test produces the same result when repeated

31
Q

what is a specific test?

A

false positive rate is low- excludes normal patients

32
Q

what is a sensitive test?

A

false negative rate is low- correctly identifies all the people with the given disorder

33
Q

what do you need to see in 3 out of the 4 chromsomes to have a quality metaphase spread?

A

see the banding resolution of certain bands in both homologues

34
Q

what is QA3 used for?

A

oncology

35
Q

what isQA4 used for?

A

if a foetus is expected to have a large structural chromosome rearrangement or aneupoloidy

36
Q

what is QA5 used for?

A

a potential abnormality detected from the second pregnancy scan. looking to exclude aneuplodies and more subtle structural rearrangements

37
Q

what is QA6 used for?

A

looking for subtle structural arrangments and microdeletions when analysing parental blood samples

38
Q

what can chronic villus samples also contain?

A

maternal contamination