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MOLECULES GENES AND DISEASE > Chromosomal abnormalities > Flashcards

Chromosomal abnormalities Flashcards

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0
Q

What is polyploidy?

A
  • Gain of a whole haploid set of chromosomes resulting in cells being triploid (69,XXX)
  • Tetraploidy is rare but can occur
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1
Q

Describe the chromosomal basis of sex determination

A
  • Mother can only produce X gametes, the father can produce either X or Y gametes
  • Therefore it is the father who determines the sex during fertilisation as either an X or Y gamete fertilises the oocyte
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2
Q

What is the cause of polyploidy?

A

-Polyspermi: fertilisation of an oocyte with more than 1 sperm

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3
Q

Is polyploidy viable?

A
  • No, it is fatal and accounts for 15% of all miscarriages

- Term deliveries die shortly after birth

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4
Q

What is aneuploidy?

A

-Loss or gain of single whole chromosomes

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5
Q

How does aneuploidy occur?

A

-Originates from non-disjunctions of a single chromosome at one of the meiotic cell divisions

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6
Q

What does non-disjunction produce?

A

-One gamete with a chromosome missing and one gamete with an extra chromosome

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7
Q

What is produced if non-disjunction occurs at a mitotic cell division?

A
  • Mosaicism. ie two cell populations in an individual

- One cell like will be normal and the other will exhibit aneuploidy

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8
Q

What 4 gametes are produced if non-disjunction occurs at meiosis I?

A

-Two gametes with an extra copy and Two gamete missing a copy

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9
Q

What are the 4 possible zygote genotypes produced when gametes produced from non-disjunction at meiosis I undergo fertilisation with a normal gamete?

A
  • 2 Trisomy gametes

- 2 monosomy gametes

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10
Q

What 4 gametes are produced if one non-disjunction occurs at meiosis II?

A
  • 2 normal gametes from the daughter cell which didn’t undergo non-disjunction
  • 1 gamete with an extra copy of a chromosome
  • 1 gamete missing a chromosome
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11
Q

What are the 4 possible zygote genotypes produced when gametes produced from non-disjunction at meiosis II undergo fertilisation with a normal gamete?

A
  • 2 normal zygotes
  • 1 zygote with monosomy
  • 1 zygote with trisomy
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12
Q

What is trisomy?

A

-Cells have an extra copy of one chromosome

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13
Q

What is monosomy?

A

-Cells have a missing copy of a chromosome

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14
Q

What is anaphase lag?

A
  • Chromosomes can get ‘left behind’ at cell division due to defects in spindle fibre attachment to chromosomes
  • The lagging chromosome may be lost entirely
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15
Q

Does anaphase lag happen in meiosis or mitosis?

A

-Both, it can happen at any stage

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16
Q

What is down syndrome?

A

-Trisomy 21 -> cells have an extra copy of chromosome 21

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17
Q

What are the signs and symptoms of down syndrome?

A
  • Hypotonia
  • Characteristic facial features
  • Intellectual disability
  • Heart defects
  • Increased prevalence of leukaemia
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18
Q

What is Edwards syndrome?

A

-Trisomy 18-> cells have an extra copy of chromosome 18

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19
Q

What causes Edward’s syndrome?

A

-Maternal meiosis II error

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20
Q

Is edwards syndrome viable?

A

-No, model lifespan is 5-15 days

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21
Q

What are the signs and symptoms of edwards syndrome?

A
  • Small lower jaw
  • Low set ears
  • Rockerbottom feet
  • Overlapping fingers
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22
Q

What is patau syndrome?

A

-Trisomy 13 -> cells have an extra copy of chromosome 13

23
Q

Is patau syndrome viable?

A

-No, majority die in neonatal period

24
Q

What are the signs and symptoms of patau syndrome?

A
  • Multiple congenital abnormalities
  • Polydactyly (extra toes etc0
  • Holosencephaly
25
Q

What is Turner syndrome?

A

-Monosomy X ->majority of cases is absent paternal X

26
Q

What are the signs and symptoms of Turners syndrome?

A
  • Only effects females
  • Short stature
  • Heart defects
  • Neck webbing
  • Mild learning disability
27
Q

What is Klinefeller syndrome?

A

-Trisomy X in males

28
Q

What is the cause of mosaicism?

A

-Mitotic non-disjunction

29
Q

What happens is the mitotic non-disjunction occurs at the first zygotic division?

A

-No mosaicism is exhibited, looks like non-disjunction meiotic event and will produce aneuploidy

30
Q

What happens if mitotic non-disjunction occurs at a division ofter the fist zygotic event?

A
  • Generation of 3 cells lines, normal, Trisomy and monosomy

- Monosomy usually lost

31
Q

What is uniparental disomy?

A

-Presence of homologous chromosomes from one parent

32
Q

What are the 3 forms of uniparental disomy?

A
  • Isodisomy -> 2 identical chromosomes from one parent
  • Heterodisomy -> 2 homologous chromosomes from one parent (most common form and occurs from meiosis I error)
  • Segmental UPD-> Only part of the chromosome involved
33
Q

What is the genetic result of uniparental disomy?

A

-The homologous chromosomes have not been imprinted and therefore the chromosome involved has no phenotypic effect

34
Q

Name 3 diseases caused by UPD

A
  • Prader-willi/angelman syndrome(15)
  • Russel-Silver(7)
  • Beckwith-Wiedemann(11)
35
Q

What is a chromosomal translocation?

A

-A chromosome abnormality caused by rearrangements of parts between non-homologous chromosomes during meiotic disjunctions

36
Q

What are the two types of translocation?

A
  • Reciprocal

- Robertsonian

37
Q

What is meant by a balanced translocation?

A

-There is even exchange of material with no genetic material extra or missing

38
Q

What is meant by an unbalanced translocation?

A

-Exchange of chromosome material is unequal producing extra or missing genetic material in cells

39
Q

What causes reciprocal translocations?

A

-Meiotic disjunction with a two-break rearrangement to produce a carrier

40
Q

What is the consequences of being a carrier of a reciprocal translocation?

A

-There is an increased risk of producing gametes with balanced and unbalanced segregations

41
Q

What possible segregations can occur in carriers of reciprocal translocations?

May need paper!

A
  • Alternate-> Alternate chromosomes have segregated together producing balanced gametes
  • Adjacent 1-> non-homologous chromosomes have segregated together producing gametes with extra chromosomal material of one chromosome and only the small loss of the other chromosome
  • Adjacent 2-> homologous chromosomes have segregated together resulting in almost an entire extra copy of one chromosome and almost entire loss of the other
42
Q

What is a robertsonian translocation?

A

-Meiotic disjunction where two acrocentric chromosomes fuse together producing a carrier with a chromosome count of 45 due to fusion

43
Q

What is the consequences of being a robertsonian translocation carrier?

A

-Phenotypically normal but with increased risk of producing aneuploidy gametes

44
Q

In reciprocal translocations, what structure forms during meiosis?

A

-Quadrivalent

45
Q

In robertsonian translocations, what structure forms during meiosis?

A

-Trivalent

46
Q

If a person carries a 14:21 robertsonian translocation, what is the possible genotype of the zygotes produced after fertilisation with a normal gamete? (monosomy, trisomy normal)

May need some paper!

A
  • Normal
  • Balanced carrier
  • Trisomy 14
  • Monosomy 14
  • Monosomy 21
  • Trisomy 21
47
Q

Why do deletions of chromosome segments occur?

A

-Due to uneven pairing or recombination

48
Q

Are deletions balanced or unbalanced?

A

-Unbalanced

49
Q

What is karyotyping?

A

-Systematic sorting of metaphase chromosomes by staining, pairing up and counting

50
Q

Why is a stain used which highlights the banding pattern of chromosomes?

A

-So each chromosome can be checked for abnormalities

51
Q

How are chromosomes reported by karyotyping?

A

-Chromosome number, sex complement, structural changes
-Separated by commas
-eg 46XX-normal female
47,XX,+21-female with trisomy 21

52
Q

What are the possible reasons for karyotype refferals?

A 
Constitutional abnormalities:
-Prenatal diagnosis
-Birth defects
-Infertility
-Abnormal sexual development
-Recurrent foetal loss
Acquired abnormalities
-Leukaemias
-Solid tumours
-Prognostic information on therapy type
53
Q

What is FISH?

A

-Fluorescence in situ hybridisation

54
Q

When is FISH used?

A
  • To identify specific chromosomes or loci (need to know what you are looking for)
  • To identify duplications or deletions of genetic material
55
Q

How is FISH carried out?

A
  • Fluorescently labelled DNA probe hybridised with target material
  • Washed
  • Visualised using fluorescent microscope
56
Q

When are chromosome paints used?

A

-To identify translocations

MOLECULES GENES AND DISEASE (12 decks)

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