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1.4 POM Genetics > Chromosomal Abnormalities > Flashcards

Chromosomal Abnormalities Flashcards

1
Q

How do you prepare a karyotype? (7)
(Big White Polar bears Will Kill Some Guys

A
  1. Collect heparinised venous blood
  2. Isolate white cells
  3. Culture in phytohaemagglutinin —> T cell growth
  4. Wait 48 hrs
  5. Add colchicine —> mitotic arrest
  6. In hypotonic saline on slide
  7. Fix and stain (giemsa)

Big —> Blood
White —> White cells
Polar bears —> Phytohaemagglutinin
Will —> Wait
Kill —> Colchicine
Some —> Saline
Guys —> Giemsa

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2
Q

What is a karyotype?

A

Visual representation of a cell’s chromosomes in order

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3
Q

Which stain is used for karyotypes?

A

Giemsa

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4
Q

What is the telomere?

A

Ends of a chromosome —> repetitive DNA sequence

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5
Q

What is the centromere?

A

Centre of chromosome —> sister chromatids join

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6
Q

What is the p-arm?

A

Short arm (top arm)

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7
Q

What is the q-arm?

A

Long arm (bottom)

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8
Q

Why is gisema staining used for chromosomes?

A

Leaves banding pattern
- Light —> more stain —> euchromatin
- Dark —> less stain —> heterochromatin

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9
Q

What are G-dark regions of chromosomes?

A

Dark bands (heterochromatin)

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10
Q

What are G-light regions of chromosomes?

A

Light bands (euchromatin)

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11
Q

What are the 4 parts of a chromosome?

A
  1. 2 Telomeres
  2. Centromere
  3. P arm
  4. Q arm
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12
Q

How are bands numbered?

A

_ _ . _
1. Band
2. Sub-band
3. Sub-sub-band
- eg. 31.2 —> Band 3, sub-band 1, sub-sub-band 2

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13
Q

What do G-dark bands contain?

A

Heterchromatin

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14
Q

What do G-light bands contain?

A

Euchromatin

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15
Q

What is bphs?

A

Bands Per Haploid Set

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16
Q

What is the difference between heterochromatin and euchromatin?

A
  • Hetero —> more compact, fewer genes
  • Eu —> more open, more genes
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17
Q

When is a karyotype usually taken?

A

Prophase

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18
Q

What is the human genome project?

A

Research project that mapped and understood all human genes

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19
Q

What is whole genome sequencing?

A

Method to determine complete DNA sequence of an organism

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20
Q

When is whole genome sequencing done?

A
  1. Cancer patients
  2. Children with suspected abnormality
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21
Q

What does ‘pter’ mean in chromosome nomenclature?

A

End of p-arm (terminal)

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22
Q

What did whole genome sequencing lead to the discovery of?

A

50-60 New genetic diseases

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23
Q

What does ‘qter’ mean in chromosome nomenclature?

A

End of q-arm (terminal)

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24
Q

What does ‘cen’ mean in chromosome nomenclature?

A

Centromere

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25
Q

What does ‘del’ mean in chromosome nomenclature?

A

Deletion

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26
Q

What does ‘der’ mean in chromosome nomenclature?

A

Derivative chromosome (contains extra material)

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27
Q

What does ‘dup’ mean in chromosome nomenclature?

A

Duplication

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28
Q

What does ‘ins’ mean in chromosome nomenclature?

A

Insertion

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29
Q

What does ‘inv’ mean in chromosome nomenclature?

A

Inversion

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30
Q

What does ‘t’ mean in chromosome nomenclature?

A

Translocation

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31
Q

What does +/- before the chromosome number mean?

A

Gail/loss of whole chromosome

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32
Q

What does +/- after the chromosome number mean?

A

Gain/loss of part of the chromosome

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33
Q

What can giemsa staining detect?

A

Chromosomal abnormalities via karyotype

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34
Q

What are the 2 types of chromosomal abnormalities?

A
  1. Aneuploidy
  2. Structural abnormalities
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35
Q

What is aneuploidy?

A

Abnormal number of chromosomes
(more/less than 2 of a homologous pair —> more/less than 46)

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36
Q

What are the 2 types of aneuploidy?

A
  1. Monosomy —> 1
  2. Trisomy —> 3
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37
Q

What is trisomy?

A

Gained one extra copy of a particular chromosome (3)

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38
Q

What is monosomy?

A

Missing one copy of a particular chromosome (1)

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39
Q

What is the purpose of meiosis?

A

Reduction from diploid to haploid —> ensure genetic variation

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40
Q

How does meiosis create genetic variation? (3)

A
  1. Random assortment
  2. Crossing over
  3. Recombination
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41
Q

How does aneuploidy arise?

A

Non-disjunction

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42
Q

Which daughter cells are effected if non-disjuntion occurs in meiosis II?

A

Only 2

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43
Q

Which daughter cells are effected if non-disjuntion occurs in meiosis I?

A

All 4

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44
Q

What types of aneuploidy does non-disjunction always result in after fertilisation?

A

Monosomy or trisomy

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45
Q

What is the most common form of aneuploidy?

A

Sex chromosome aneuploidy

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46
Q

What is the prevalence of sex chromosome aneuploidy?

A
  1. 1/400 males
  2. 1/650 females
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47
Q

Why may X chromosome aneuploidy be tolerated?

A

X-inactivation of excess X chromosomes (only 1 active)

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48
Q

Why may Y chromosome aneuploidy be tolerated?

A

Low gene content of Y chromosome

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49
Q

What is the PAR of sex chromosomes?

A

Pseudo-autosomal region
- Influence non-sex traits eg. immune system

50
Q

Why does sex chromosome aneuploidy still have some effect even when the extra chromosome is inactivated? (2)

A

PAR in X and Y needed

51
Q

When does X chromosome aneuploidy cause an effect? (3)

A
  1. Division of odd number —> not tolerated
  2. Not all excess X chromosome inactive
52
Q

What is an example of aneuploidy?

A

Trisomy 21

53
Q

What does trisomy 21 cause?

A

Down’s Syndrome

54
Q

What is the karyotype of individuals with trisomy 21?

A

47 + 21

55
Q

How does trisomy 21 usually arise?

A

Maternal non-disjunction

56
Q

What is maternal age effect?

A

Correlation between mother age and effects on offspring

57
Q

What is the maternal age effect of trisomy 21?

A

Older mum —> more likely trisomy 21 child

58
Q

What is oogenesis?

A

Development of ovum in ovaries

59
Q

When is oogenesis completed?

A

Fertilisation

60
Q

What are the 3 stages of oogenesis?

A
  1. Oogonium mitosis —> primary oocyte
    - Baby in utero
    - Paused in prophase I till puberty
  2. Oocyte meiosis I —> secondary oocyte + polar body
  3. Oocyte meiosis II —> ovum + polar body
    - Paused in metaphase II —> ovulation
    - Completed if fertilised
61
Q

Why does an increased maternal age increase the risk of trisomy 21 specifically?

A

Increased risk of maternal non-disjunction

62
Q

How many mitotic divisions occur to primary spermatocytes per year?

A

23

63
Q

What is the paternal age effect?

A

Correlation between father age and effects on offspring

64
Q

Why does an increased maternal age increase the risk of some gene disorders?

A

Degradation of factors holding homologous chromatids together over time —> chromatids don’t align at mitotic equator

65
Q

What do egg and sperm cells start as?

A
  1. Egg - oogonium —> oocyte
  2. Sperm - spermatogonial stem cells —> spermatocyte
66
Q

What are the products of the 2 divisions of a primary oocyte?

A

Ovum + 3 polar bodies

67
Q

Is there a paternal effect on aneuploidy?

A

No

68
Q

Which disorders have a paternal age effect?

A

Single gene disorders

69
Q

What are 3 examples of gene disorders with paternal age effect?

A
  1. RET
  2. FGFR2
  3. FGFR3
70
Q

Which 3 gene mutations have a paternal age effect?

A
  1. Pfeiffer
  2. Apert
  3. Crouzon
71
Q

What enhances the paternal age effect?

A

Selfish spermatogonial selection

72
Q

What does selfish spermatogonial selection refer to?

A

Certain mutations have a selective advantage to the spermatogonial stem cells

73
Q

What is a paternal risk factor for aneuploidy?

A

Smoking

74
Q

What proportion of still births and spontaneous abortions are a result of aneuploidy?

A
  • 5% of still births
  • 50% of spontaneous abortions
75
Q

How prevalent is aneuploidy?

A

5% of all pregnancies

76
Q

When can trisomy of any chromosome be detected?

A

Prenatally

77
Q

Why does trisomy often lead to still births or spontaneous abortions?

A

Most not compatible with life

78
Q

Which 3 trisomies are compatible with life?

A
  1. 21
  2. 18
  3. 13
79
Q

Is aneuploidy usually compatible with life?

A

No

80
Q

What is genetic mosaicism?

A

Presence of populations of cells with 2 or more different genotypes

81
Q

What proportion of the population is thought to have genetic mosaicism?

A

100% —> everyone

82
Q

What are the 2 causes of genetic mosaicism?

A
  1. Non-disjuncture in early development
  2. Loss of extra chromosome in early development
83
Q

What can mosaicism in aneuploidy lead to?

A

Lethal aneuploidy becoming survivable
- eg. Trisomy 8 or 9

84
Q

What are the most common genetic mosaics?

A

45, X

85
Q

When does crossing over occur?

A

Prophase I of meiosis

86
Q

What are the 2 stages of crossing over?

A
  1. Pairs of chromosomes align
  2. Chiasma forms —> cross over
87
Q

How many times does crossing over occur per chromosome per meiosis?

A

1-3

88
Q

What does crossing over increase?

A

Genetic diversity

89
Q

What is a chiasma?

A

Location of chromatids crossing over

90
Q

When does crossing over lead to genetic abnormalities?

A

Unequal crossover (chromatids misalign —> chromosome with duplication and deletion)

91
Q

What are the 3 results of unequal cross over?

A
  1. Duplication
  2. Deletion
  3. Inversion
92
Q

What is chromosome deletion?

A

Part of a chromosome is missing or deleted

93
Q

What is chromosome duplication?

A

Portion of a chromosome is copied —> extra genetic material

94
Q

What is the most common result of unequal cross over?

A

Paracentric inversion

95
Q

What is chromosome paracentric inversion?

A

Rearrangement of chromosomal segments in one same arm (doesn’t include centromere)

96
Q

What does paracentric inversion lead to? (2)

A
  1. Usually unaffected carriers (may have reproductive problems)
  2. Children with deletions/insertions
97
Q

How can structural chromosomal abnormalities of carriers impact their offspring?

A

Partial trisomy or monosomy

98
Q

How can paramentric inversion influence cancer?

A

t(9;22)(q34;q11) in Philadelphia chromosome

99
Q

Are most structural chromosomal abnormalities inherited?

A

No - most de novo

100
Q

How can chromosomal deletions be detected?

A

Microscope
- Microdeletion —> v. high resolution banding

101
Q

What are 2 examples of chromosomal deletion disorders?

A
  1. Cri-du-chats syndrome - 46,del(5p)
  2. Williams syndrome
102
Q

What type of disorder is Cri-du-chat syndrome?

A

Chromosomal deletion

103
Q

What is the karyotype of Cr-du-chat syndrome?

A

46,del(5p)

104
Q

What is an example of a chromosomal microdeletion disorder?

A

DiGeorge syndrome

105
Q

What type of disorder is DiGeorge syndrome?

A

Chromosomal microdeletion

106
Q

What is the karyotype of DiGeorge syndrome?

A

22q11.2 del

107
Q

What type of disorder is Williams syndrome?

A

Chromosomal deletion

108
Q

What are the 5 symptoms of Williams syndrome?

A
  1. Long philtrum
  2. Short, upturned nose
  3. Arched eyebrows
  4. Supravalvular aortic stenosis
  5. Cocktail party personality (no social anxiety)
109
Q

What is Williams syndrome genetically?

A

7q11.23 deletion

110
Q

How is Williams syndrome detected and why?

A

FISH (fluorescent in situ hybridisation) —> detects lack of elastin
- Deletion too small

111
Q

What are the 6 symptoms of 7q11.23 duplication syndrome?

A
  1. Broad nose
  2. Short philtrum
  3. Flat eyebrows
  4. Aortic dilation
  5. Autistic behaviours
  6. Delayed speech development
112
Q

Do duplications or deletions of the same chromosome have a milder phenotype?

A

Duplications —> less effect

113
Q

What is Robertsonian translocation?

A

Translocation in acrocentric chromosomes resulting in a single chromosome with 2 q arms

114
Q

What are the 3 classes of chromosomes?

A
  1. Metacentric —> p=q
  2. Submetacentric —> p<q
  3. Acrocentric —> no p
115
Q

Which class of chromosomes can undergo Robertsonian translocation?

A

Acrocentric

116
Q

Which 5 chromosomes are acrocentric?

A

13, 14, 15, 21, 23

117
Q

What are the 3 most common Robertsonian translocations?

A
  1. 13 and 14 join
  2. 14 and 15 join
  3. 14 and 21 join (think multiple of 7)
118
Q

What is usually the effect of Robertsonian translocations and why?

A

No effects
- No genetic material lost

119
Q

What does chromosomal balance refer to?

A

Whether the genetic material in a chromosome in correct proportions
- Unbalanced —> genetic abnormalities

120
Q

What does ‘rob’ mean in chromosome nomenclature?

A

Robertsonian translocation

1.4 POM Genetics (9 decks)

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