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PoD > Chromosomes and abnormalities > Flashcards

Chromosomes and abnormalities Flashcards

1
Q

Basic structure of chromosomes

A
  • Linear chromosomes
  • Telomere
  • Centromere
  • Chromatin
  • Extragenic sequences
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2
Q

Telomere

A
  • Bits at end
  • Repetitive nucleotide sequences at end which protect chromosome from deterioration or from fusion with neighbouring chromosomes
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3
Q

Centromere

A
  • Bit in middle
  • Constricted region that links sister chromatids. Held together by cohesion
  • Has repetitive DNA sequences such as satellited DNA
  • Side of kinetochore, core where there is microtubule attachment from spindles
  • Protein complex that binds to microtubules
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4
Q

Chromatin

A
  • DNA packaged with histone proteins into units called nucleosomes
  • Histones have +ve change
  • Heterochromatin
  • Euchromatin
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5
Q

How DNA is packaged

A
  • Nucleosome -> chromatin fibre -> fibre-scaffold complex -> chromsome
  • Negatively charged DNA neutralised by positively changed histone proteins
  • DNA takes up less space
  • Inactive DNA can be folded into inaccessible locations until required
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6
Q

Chromosome structure

A
  • 2 sisters
  • q (longer) arm and p (shorter) arm
  • Banding can define each chromosome
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7
Q

Metacentric

A

Far away from centre

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8
Q

Submetacentric

A

Closer to centre

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9
Q

Acrocentric

A

Petit arm is entirely occupied by heterochromatin

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10
Q

Extragenic sequences

A
  • Tandemly repeated DNA sequences: satellite and mini-satellite
  • Both non-coding DNA
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11
Q

Satellite DNA

A
  • at centromeres and telomeres

- A-T rich DNA, separates in a different place

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12
Q

Minisatellite DNA

A
  • DNA used for DNA fingerprinting
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13
Q

Cell cycle and cell division

A

G1, gap phase, cell grows
S, replication of DNA
G2, gap phase, cell prepares to divide
Mitosis

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14
Q

Stages of mitosis

A
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
  • Cytokinesis
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15
Q

Prophase

A
  • Chromosomes condense
  • Nuclear membrane disappears
  • Spindle fibre form from the centriole
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16
Q

Metaphase

A
  • Chromosomes aligned at the equator of the cell
  • Attached by fibre to each centriole
  • Maximum condensation of chromosome
17
Q

Anaphase

A
  • Sister chromatids separate at centromere
  • Separate longitudinally
  • Move to opposite ends of cells
18
Q

Telophase

A
  • New nuclear membranes form

- Each cell contains 46 chromosomes (diploid)

19
Q

Cytokinesis

A
  • Cytoplasm separates

- 2 new daughter cells, receive complete and precise copies of genomes

20
Q

Meisosis

A
  • Cell divisions in germ cells
  • Diploid cells divide to form haploid cells
  • Chromosomes are passed on as rearranged copies: creats genetic diversity, recombination between homologs is defining event in sexual reproduction
21
Q

Gametogenesis. Male vs. female

A
  • Female: happens for years from early embryotic life

- Male: takes a matter of days

22
Q

How to chromosome analysis

A
  • Blood sample
  • Separate off red cells
  • Add culture medium to white cell suspension
  • Incubate
  • Colchicine-microtubule inhibitor added
  • Cells assemble in mitosis, increases population of cells
  • Hypotonic saline added
  • Cells fixed and stained
  • Karyotyped (meta, sub-meta and acrocentric. Chromosomes are numbered in size order)
23
Q

FISH

A
  • Fluorescent in situ hybridisation
  • For looking at a sequence of specific interest
  • Take a fragment of DNA sequence you’re interested in and labelled using fluorescent dye
  • Denature and hybridise the DNA to find the DNA you’re interested in
24
Q

Types of FISH

A
  • Unique sequence probes
  • Centromeric probes: useful for chromosome number
  • Telomeric probes: useful for detecting subtelomeric rearrangements, useful for children with unexplained mental retardation
  • Whole chromosome probes: cocktail of probes covering different parts, translocations and rearrangments
25
Q

3 basic types of chromosomal abnormalities

A
  • Numerical
  • Structural
  • Mutational
26
Q

Numerical chromosomal abnormalities

A
  • Trisomy, 3 of the same chromosomes

- Monosomy, only one X chromosome

27
Q

Trisomy examples

A

Autosomal aneuploidy syndrome: trisomy 13: Patau, dysmorphic, mental retardation. Trisomy 18: Edwards, severe developmental.
Sex chromosomes aneuploidy syndromes: 47, XXY. Male but infertile, small testes

28
Q

Monosomy example

A
  • Only one X chromosome.

- 45,X Females of short stature, infertile. Inteligent. Normal life span

29
Q

Structural chromosomal abnormalities

A
  • Wrong arrangement
  • Balanced or unbalanced translocations
  • Deletions
  • Insertions
  • Inversions
30
Q

Balanced translocations

A
  • All genetic information is still present

- 2 chromosomes of different size translocate

31
Q

Reciprocal translocation

A
  • Breaks in 2 chromosomes with formation of 2 new derivative chromosomes
  • If a reciprocal translocation carrier is fertilised by a normal gamete 1/4 chance normal, 1/4 chance balanced and 1/2 chance unbalanced
  • Unbalanced means partial trisomy and monosomy
32
Q

Robertsonian translocation

A
  • fusion of 2 acrocentric chromosomes

- 2 chromosomes are fused but no genetic info is lost, 2 short arms are lost

33
Q

Deletions

A

Break in the chromosome and there is genetic material deleted

34
Q

Inversions

A
  • Paracentric inversion: break in the chromosome and there is an inversion of the centromere and reinserted
35
Q

Origin of chromosome abnormalities

A
  • Non-disjunction
  • Meiosis I
  • Meiosis II
  • Abnormalities are most common from maternal meiotic as eggs sit for decades in meiosis I phase and the disjunction process becomes less accureate

PoD (33 decks)

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