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MBD > Structural Chromosomal Abnormalities* > Flashcards

Structural Chromosomal Abnormalities* Flashcards

1
Q

What are some examples of structural abnormalities?

A
  • Translocation
  • Inversion
  • Deletion
  • Duplication
  • Rings
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2
Q

What are the two types of translocational abnormalities?

A
  • Reciprocal and robertsonian
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3
Q

What is translocation?

A
  • Exchange of two segments between non homologous chromosomes
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4
Q

What is the main reason translocation takes place?

A

Inappropriate non-homologous end joining (NHEJ)

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5
Q

What is non-homologous end joining?

A
  • DNA repair mechanism that repairs double stranded breaks by literally just sticking them back together
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6
Q

How is a derivative chromosome created?

A

Broken bits of chromosome being stuck back on the wrong chromosome

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7
Q

What is balanced translocation?

A

There is non-homologous end joining but because the net amount of DNA in a cell hasn’t changed, it doesnt matter

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8
Q

What is the philadelphia chromosome?

A

Philadelphia chromosome is an exchange between Cr9 and Cr22

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9
Q

What does the philadelphia chromosome cause?

A
  • The activation of the oncogene nature of the gene

→ Leads to types of leukaemia and myeloma

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10
Q

What is the philadelphia chromosome formed from?

A

Non-homologous end joining between a proto-onco gene on chromosome 9 and a gene on chromosome 22

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11
Q

How are unbalanced individuals produced?

A

Tetravalent structure formed instead of a bivalent structure

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12
Q

What is a tetravalent structure formed from?

A

Two normal chromosomes and two chromosomes that have undergone inappropriate non-homologous end joining

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13
Q

What do unbalanced individuals cause?

A

Essentially trisomic for one end of the chromosome and monosomic at the other end

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14
Q

What are the results of unbalanced reciprocal translocation?

A
  • May lead to miscarriage
  • Learning difficulties/physical difficulties

Very person-specific so clinical features vary

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15
Q

Where is the only place robertsonian translocation can happen?

A

With acrocentric chromosomes that carry specific sets of copies of rRNA

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16
Q

What happens if you loose chromosomes in robertsonian translocation?

A

Nothing

17
Q

What is a robertsonian chromosome?

A

Two chromosomes that can stick together with a single centromere

18
Q

How many chromosomes does a balanced carrier have?

A

45

19
Q

What has happened if there are 46 chromosomes including a robertsonian?

A

Unbalanced carrier

20
Q

What are the products of normal mitosis, reciprocal and robersonian?

A
  • Normal - two bivalents
  • Reciprocal - quadrivalent
  • Robertsonian - trivalent
21
Q

What is a terminal deletion?

A

Loss of tetrameric chunks

22
Q

What is an interstitial deletion?

A

Loss of a chunk of chromosome in the middle of an arm

23
Q

What are some examples of interstitial deletions?

A

Prader-willi
Digeorge syndrome
Cri du chat

24
Q

What do deletions cause?

A

A region of monosomy

25
Q

Where are gross deletions seen?

A

Metaphase spread on G-banded karyotype

26
Q

Why do deletion/duplication events generally happen?

A

Unequal crossing over

27
Q

What are the steps of chromosome staining?

A

Blood sample taken
Add phytohaemagglutinin and culture medium
Culture at 37 deg celcius for 3 days
Add colchicine and hypotonic saline
Cells fixed
Spread cells onto slide by dropping
Digest with trypsin and stain with giemsa
Analyse and karyotype

28
Q

What are the steps in fluorescent in situ hybridisation (FISH)?

A

Culture cells and metaphase spread
Add fluorescent probe
Denature probe and target DNA
Mix probe and target DNA
Probe binds to target

29
Q

What are the components of PCR?

A

Template
Primers
Polymerase
Nucleotides
Buffer
MgCl2

30
Q

What is non-invasive prenatal testing?

A

Taking fetal DNA from maternal blood

MBD (23 decks)

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