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MLSCI 480 > Chromosomes & Karyotyping > Flashcards

Chromosomes & Karyotyping Flashcards

1
Q

Chromatin

A
  • DNA, histones and other proteins = chromosome
  • plays important role in DNA compaction, regulating replication, transcription, recombination and chromosome segregation
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2
Q

Nucleosome

A
  • 147 bp of DNA wrapped around octomer (two H2A-H2B dimers bound to an H3-H4 tetramer) and joined by linker DNA (34 bp)
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3
Q

Nucleosome histone core

A
  • 8 histones/ octamer
  • two of: H2A, H2B, H3, H4
  • nucleosome core DNA = 147 bp of DNA wrapped around octamer
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4
Q

Nucleosome function

A
  • Facilitates the compaction of ~200 bp of DNA
  • Facilitates the compaction of the 30 nm chromatin fiber
  • Template for chromatin enzymes which facilitate post-translational modifications = PTM facilitate higher levels of compaction
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5
Q

Chromatosome

A
  • consists of a nucleosome and a linker histone
  • Histone protein H1 may bind to linker DNA = protect an additional 15 to 20 bp of DNA
  • H1 bind at the DNA entering & exiting the nucleosome
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6
Q

Histone tails

A
  • Open for post-translation modification = changes chromosome structure
  • Lysine and Arginine groups

Acetylation = less compact for transcription
Methylation = condensed

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7
Q

Heterochromatin

A

Eukaryotic chromatin remains tightly compacted during interphase and is not transcribed

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8
Q

Euchromatin

A

less condensed eukaryotic chromatin that is available for transcription

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9
Q

Phase in Cell Cylce used for Karyotyping vs FISH

A
  • Karyotyping = metaphase (most condensed)
  • FISH = interphase (not as condensed for fluorescent probes to attach)
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10
Q

Sister chromatids

A

In metaphase = one duplicated chromosome

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11
Q

Homologous chromosomes

A

Pair of sister chromatids from each parent (maternal and paternal)

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12
Q

Telomere vs Centromere

A

Telomere:
- end of a chromosome composed of repeated DNA sequences and associated proteins

Centromere:
- constriction in metaphase chromosomes.
- composed of repeated sequences, where chromosome that attaches to the mitotic spindle

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13
Q

p arm vs q arm

A

p arm: petite arm

q arm: long arm

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14
Q

Differentiate Metacentric, Sub metacentric, Acrocentric, Telocentric

A

Metacentric: centromere located centrally, the p and q arms are approximately the same length.

Sub metacentric: the centromere is located off center; the q arm is slightly longer than the p arm

Acrocentric: the centromere is located nearer one end of the chromosome; the q arm is significantly larger than the p arm

Telocentric: centromere is the distal end of the chromosome and there is no p arm; not normally found in humans

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15
Q

G-banding

A
  • karyotype used to ID chromosome abnormalities in genetic diseases and cancers
  • differentiate by size, shape and banding patterns

Giemsa stain:
Light areas = Euchromatin
Dark = heterochromatin
Unstained centromeres

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16
Q

WIP Resolution of G-banded chromosomes based on phase

A
  • towards metaphase is easier to read
  • towards prophase has better separation of bands
17
Q

How are bands on chromosomes numbered?

A
  • Starts from the centromere and counts outwards

Chromosome> Arm > region > bands > subband
ie. 17q11.2

18
Q

Aneuploidies vs Structural abnormalities

A

Aneuploidies: abnormal number of chromosome, ie. trisomy

Structural: translocations, deletions, insertions, inversions, isochromosomes, ring chromosomes

19
Q

What is a balanced translocation ?

A

Two chromosomes that have a double-sided break
- no loss or gain of genetic material

20
Q

Isochromosomes

A
  • two chromosomes become one = two p arms or two q arms separate together
  • loss and gain of genetic material = unbalanced structural abnormality
21
Q

Unbalanced Translocation

A
  • results from a balanced translocation carrier and normal chromosome
  • gain or loss of genetic material

1/4 chance of:
- normal chromosomes

  • balanced translocation carrier
  • unbalanced duplication-deletion
  • unbalanced duplication- deletion
    NOTE: miscarriage
22
Q

FISH

A

Fluorescence in situ Hybridization:

  • DNA probes specific for nucleotide sequences
  • probes made of DNA/ RNA fragments (100-1000bp)
  • modified nucleotides in probes fluorescence under certain conditions
23
Q

FISH whole-chromosome probes

A

Collections of smaller probes, each of which binds to a different sequence along the length of a given chromosome

24
Q

FISH using SKY

A

Spectral karyotyping:
24 chromosome-specific painting probes are used in just one FISH experiment Very expensive (not used often)

25
Q

FISH: centromeric probes

A
  • can be used on interphase and metaphase chromosomes
  • used to enumerate chromosomes
26
Q

FISH using Locus specific probes

A
  • bind to a particular region of a chromosome
  • useful when scientists have isolated a small portion of a gene and want to determine on which chromosome the gene is located
    OR
  • how many copies of a gene exist within a particular genome
27
Q

FISH using CNV probes

A

Copy Number Variation probes (locus specific):
- designed to hybridize to a precise gene location
- used to identify gene deletions and amplifications

28
Q

FISH using Gene Fusion Probes

A
  • locus specific
  • fusions occur when two normally separated genes are joined = show the signals less than one signal width apart
  • a normal cell will display the colors as separate signals
29
Q

FISH using Break-apart probes

A
  • locus specific
  • single probe with 2 fluorophores
  • probe targets two areas of a specific gene sequence
  • Intact = probe appears yellow
  • Apart = red signal and a green signal are seen
30
Q

Name the nucleosome histones

A

Two of: H2A, H2B, H3, H4

31
Q

List the levels of compaction of chromatin

A

DNA > histones > nucleosome > chromatin > 30nm fibre > looped domains > metaphase chromosome

32
Q

Karyotype of a normal female vs male

A

46,XX = female
46, XY = male

33
Q

Karyotype of trisomy female

A

47,XX+21

34
Q

Purpose of Colcemid for Karyotyping

A

Arrests cells in metaphase

35
Q

Purpose of trypsin in Karyoptyping

A

Digests proteins (so stain can attach)*

*NOTE: in Giemsa staining

36
Q

Stain for chromosomes

A

Giemsa stain

MLSCI 480 (21 decks)

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