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Karan - MBBS Year 1: Principles Week 2 > Genes, Chromosomes and Cell Division > Flashcards

Genes, Chromosomes and Cell Division Flashcards

1
Q

How are chromosomes organised?

A
  • 22 pairs of homologous autosomal chromsomes identical in shape, size and number of genes
  • 1 pair of sex chromosomes - heterologous
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2
Q

Define cytogenetics and what does it allow.

A
  • Study of chromosomes and chromosomal abnormalities
  • Allows visualisation of chromosomes e.g centromere position
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3
Q

Why is visualisation easier when the chromosomes are in metaphase?

A
  • Chromosomes are condensed
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4
Q

Describe cytogenetic processing.

A
  • Hypotonic solution added - causes nuclear swelling
  • Staining to view bands
  • Produces a karyogram
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5
Q

Give an example of banding used in karyotyping and what it can be used for.

A
  • EXAMPLE: Giemsa banding
  • Allows detections of rearrangements or deletions
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6
Q

What does 14q32 mean on a karyogram?

A
  • Second band in 3rd region of long arm of chromosome 14
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7
Q

Describe FISH.

A
  • Chromosomal DNA is unwound and separated into single strands
  • Fluorescently labelled DNA probes bind to chromosomes
  • Visualised under microscope
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8
Q

What can FISH be used for?

A
  • Detect microdeletions or microinsertions
  • Visualise chromosome organisation
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9
Q

Describe CGH.

A
  • DNA extracted from specific patient cells and labelled green
  • Reference DNA labelled with red fluorescent molecules
  • Combine equal amounts and hybridise onto normal metaphase DNA array
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10
Q

How can CGH be used to detect chromosomal abnormalities?

A
  • ABNORMALITY if ratio of green to red is unequal
  • Can detect type/severity of cancers by scanning for deletions/duplications
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11
Q

Describe Array CGH and what are its advantages

A

.- Detects missing or duplicated pieces of chromosome
- Better resolution than FISH - detects microdeletions affecting only a single gene
- Can look at whole genome using small amount of DNA

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12
Q

What are the disadvantages of Array-CGH?

A

Cannot detect balanced chromosomal translocations

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13
Q

What is DNA sequencing used for?

A
  • Determination of linear order of nucleotides of DNA
  • Detection of indel mutations
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14
Q

How does DNA sequencing work?

A
  • Complementary bases labeled by fluorescent dye specific for nitrogenous bases
  • Specific nucleotides detected by colour
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15
Q

What are meiotic nondisjunctions?

A
  • Two chromosome homologs migrate to same daughter cells instead of disjoining and migrating to different cells
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16
Q

Define aneuploidies.

A
  • Missing or additional individual chromosomes due to nondisjunction
17
Q

What is monosomy and trisomy?

A

MONOSOMY - one copy of chromosome in diploid cell
- TRISOMY - three copies

18
Q

Describe Down Syndrome.

A
  • TRISOMY 21 - Autosomal aneuploidy
19
Q

What can trisomy 21 problems cause?

A
  • Greater instances of heart septal defects, hypothyroidism, leukaemia etc.
20
Q

Describe how Trisomy 21 (T21) conditons are diagnosed.

A
  • Second trimester screening for AFP, hCG and the estriol steroid
  • If baby at high risk, mother offered amniocentesis and chorionic villus sampling done by karyotyping/FISH
21
Q

Describe Edward’s Syndrome.

A
  • TRISOMY 18 - Autosomal aneuploidy
  • Causes heart, GI and CNS defects
  • Diagnosed through karyotyping
  • Major cause of death is cardiac/respiratory failure - half don’t survive beyond first week
22
Q

Describe Patau’s Syndrome.

A
  • TRISOMY 13 - Autosomal aneuploidy
  • Polydactyly, brain and spinal cord defects
  • Diagnosed by karyotyping
  • Prognosis is poor (80% don’t survive beyond one month)
23
Q

Describe Turner’s Syndrome and how it can be inherited.

A
  • X chromosome monosomy - sex chromosome aneuploidy
  • Usually offspring receives X chromosome only from mother
  • Absence of paternally derived sex chromosome during early mitosis in embryo/during meiosis in father caused by nondisjunction
24
Q

What are the clinical features of Turner’s Syndrome?

A
  • Affects females
  • Ovarian dysgenesis
  • Hand and feet lymphoedema
  • Congenital heart defects
25
Q

Describe Klinefelter’s Syndrome.

A
  • Karyotype: 47, XXY
  • Clinical features include hypogonadism, infertility, gynaecomastia
  • X is from mother in 50% (NONDISJUNCTION AT MEIOSIS)
  • Mosaicism in 15%
26
Q

What is the difference between an unbalanced and balanced chromosome abnormalities?

A
  • UNBALANCED - rearrangement causes gain or loss of chromsomal material
  • BALANCED - does not do this
27
Q

Describe reciprocal translocation

A
  • TRANSLOCATION - interchange of genetic material between nonhomologous chromosomes
  • Occurs during meiosis
  • Breaks occur in 2 different chromosomes and material mutually exchanged
28
Q

What is the result of reciprocal translocation?

A
  • Inherit balanced/unbalanced translocation i.e partial trisomy/monosomy
29
Q

Describe Robertsonian translocation

A
  • Long arms fuse at centromere - form single chromosome
  • Offspring may inherit missing chromosomes or extra long arm
30
Q

Descibe insertion.

A
  • One chromosome passes genetic material to another without reciprocal exchange
31
Q

Describe inversions.

A
  • Chromosome segment reversed end to end
  • Single chromosome undergoes 2 breaks and reinserted in inverted order
  • Can be peri- or paracentric
  • Structural arrangements are balanced so carrier asymptomatic
32
Q

How can inversions affect meiosis?

A
  • Interfere with lining up of chromosomes
  • Results in duplications/deletions in chromosomes of daughter cells
33
Q

What is somatic mosaicism?

A
  • Chromosome rearrangements in somatic cells
  • Can cause cancer
34
Q

Describe the Philadelphia chromosome.

A
  • Translocation of most of C22 to long arm of C9
  • Distal portion of 9q translocated to C22
  • Protooncogene called ABL moved from normal position from 9q to 22q
  • Alters ABL gene product - increased tyrosine kinase activity and malignancy in hamapoetic cells

Karan - MBBS Year 1: Principles Week 2 (12 decks)

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