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Y2 EMS- Theme 2- Genetic And Environmental Causes Of Disease > 5. Chromosomal Pathology > Flashcards

5. Chromosomal Pathology Flashcards

1
Q

In what percentage of live births are chromosome abnormalities found

A

0.7%

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2
Q

What percent of stillbirths are chromosome abnormalities found in

A

5%

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3
Q

What percent of pregnancy losses are chromosomal abnormalities found in

A

50%

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4
Q

What is dosage effect

A

Number of copies variation = CNV

Loss is usually worse than gain

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5
Q

What can deletion of one chromosomal homologue result in

A

Unmasking of a recessive disorder

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6
Q

Diploidy meaning

A

Normal state of chromosome number

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7
Q

Anuploidy meaning

A

1 or more extra or missing chromosomes eg, trisomy, monosomy

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8
Q

What do aneuploidys result from

A

Meotic errors:

  • usually in the mother during oegenesis
  • can occur during spermatogenesis
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9
Q

What is the effect of maternal age on chance of autosomal trisomies.

A

Increases autosomal trisomes

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10
Q

What is Down’s syndrome caused by

A

An extra copy of chromosome 21= trisomy 21

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11
Q

What would 47,XX +21 denote

A 
Person has 47 chromosomes 
Including XX (female)
One extra ch. 21 = Down’s syndrome
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12
Q

How do chromosome errors occur in Meiosis

A

Abnormalities in how the chromosomes segregate from one another in meiotic divisions

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13
Q

What is non - disjunction (in mieotic errors)

A

Failure of chromosome or chromatid speration

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14
Q

What happens in meiosis error I in a non disjunction

A

Both of the chromosomes segregate into a single cell rather than one into each cell
- gives rise to two disomic gametes and two nullsomic gametes

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15
Q

What happens in in a mieosis II error

A

Chromatid non disjunction - the two sister chromatids from one of the cells doesn’t separate properly
- results in one disomic, one nullisomic, two normal gametes

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16
Q

Disomic and normal gamete can result in

A

Fetal trisomy (may be viable)

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17
Q

Monosomic (none) and normal can result in

A

Fetal monosomy (lethal)

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18
Q

Name three viable autosomal trisomies

A

Down’s syndrome = t21
Patau syndrome = t13
Edwards syndrome = t18

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19
Q

Symptoms of Down’s syndrome (trisomy 21)

A 
Heart malformations 
Learning difficulties 
Gut atresia 
Early dementia 
Leukaemia 
1/700
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20
Q

Symptoms of patau syndrome (trisomy 13)

A 
Microcephaly 
Severe 
Holopresencecephaly = brain dev. Abnormalitiy
Clefting 
Polydactyly 
Rare (1/5000)
Unlikely long term survival
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21
Q

Symptoms of trisomy 18 = Edwards syndrome

A 
Microcephaly 
Clenched hands 
Rocker bottom feet 
Cardiac anomalies 
1 in 5000
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22
Q

Polydactyly is symptom of which trisomy

A

Patau syndrome (T13)

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23
Q

Rocker bottom feet and clenched hands are symptoms of whihc trisomy

A

Edwards syndrome = T18

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24
Q

If all anueploidies are possible, why are only 13, 18 and 21 viable and the rest lethal

A

The genes on these chromosomes (13, 18, 21) are less dosage intolerant

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25
Q

What happens in sex chromosome aneuploidy in regards to X inactivation

A

One X chromosome is inactivated cos of dosage compensation

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26
Q

What is the Karyotype for Turner Syndrome (sex ch. aneuploidy)

A

45, X (only one X chromosome)

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27
Q

Does Turner syndrome affect males and females

A

Females

28
Q

Symptoms of Turner Syndrome

A 
Short stature 
Infertility - primary ammenorrhea = absence of menstruation
Foetal/ neonatal oedema 
Neck webbing 
Aortic coarctation 
1/2500
29
Q

Chromosomes in Klinfelter syndrome

A

47, XXY (males born with extra X chromosome)

30
Q

Does klinfelter syndrome affect males or females

A

Males

31
Q

Symptom of klinfleter syndrome

A

Male infertility

32
Q

Polyploidy meaning

A

Whole extra haploid set of 23 chromosomes

33
Q

Give two examples of when polyploidy is seen

A

Cancer cells
Abnormal conception in pregnancy
(Errors at fertilisation, extra chromosomes can be paternal or maternal)

34
Q

What percentage of all pregnancies does polyploidy occur in

A

2%

35
Q

What is digyny

A

When an unreduced maternal gamete (2n, sister chromatids haven’t separated properly) fertilises a reduced (normal, haploid) paternal gamete
= maternal extra chromosome

36
Q

Symptoms of digyny

A

Growth retardati on in foetus and placenta and more

37
Q

What is dispermy

A

Extra paternal chromosomes

2n from father but normal n from mother

38
Q

Deletion meaning

A

Loss of chromosome segments

39
Q

Duplicate meaning

A

Gaining extra chromosome material

40
Q

Mosaicism meaning

A

Two or more cell populations with a different genotype exists in an organism

41
Q

What is FISH and what is it sued for

A

Fluorescent in situ hybridisation

- can visualise and map the genetic material in cells, including specific genes or portions of genes

42
Q

How does FISH work

A
  1. Prepare short sequences of single stranded DNA that match the portion of the gene you’re interested in/ looking for = probes.
  2. Label the probes each with a different colour of Florescent dye
  3. Since these probes are single stranded, they will bind to the persons complementary strand of DNA, wherever it resides on the individuals chromosomes.
  4. Therefore, the fluorescent tag provides a way for researchers to see its location.
43
Q

What is G-banding used for

A

Technique used in cytogenetic to produce a visible karyotype by staining condensed chromosomes - useful for identifying genetic diseases through the photographic representation of the entire chromosome complement.

44
Q

What is whole genome sequencing

A

Method for analysing entire genomes

45
Q

Advantages of WGS

A
  • provides high resilsltion, base by base view o the genome
  • captures large n small variants that may be missed with targeted approaches
  • identifies potential causative variants
  • gives large volumes of data in short time
46
Q

What kinds of things can WGS detect

A

Single nucleotide variants, insertions/ deletions, CNV, large structural variants

47
Q

What is chromosomal microarray

A

Looks for CNVs:
Duplications and deletions
( eg, trisomy such as Down’s syndrome, monosomy)

48
Q

How does microarray work

A

Probes and the patients DNA are hybridised

  • probes bond to specific chromosome regions
  • computer analysis is sued to compare n=genetic material with the reference sample - difference = variant
49
Q

What is QF- PCR

A

Quantitative Fluorescent PCR is a molecular test for the identification of common aneuploidy syndromes: 13, 18, 21

50
Q

How does QF- PCR work

A

Specific DNA markers (Short Tandem Repeats) are found across the chromosomes.
In this method, 3-5 STR markers across chromosomes 13, 21, 18 are amplified by PCR
The primers used for amplification are have different coloured fluorescent tags and the amplification products are different sizes.
The amount of fluorescence and size of DNA that’s been copied is measured and presented graphically.
Number of peaks/ height of each peak shows teh number of copies of alleles at that region of the chromosome in that DNA sample.

51
Q

What test can be used to test for DiGeorge syndrome

A

FISH as it can detect micro deletion

(DiGeorge syndrome has 2- Mb deletion of chromosome 22q11.2

52
Q

Does fish or g banding have higher resolution

A

Fish

53
Q

What is a novel junction

A

Place where the extra genetic material meets the existing one in duplication of a gene

54
Q

Which molecular test is important for during pregnancy

A

QF PCR

55
Q

What is a pericentric inversion

A

If both breakpoints are on different arms

‘Around the centromere’

56
Q

Inversion meaning

A

When DNA breaks away and attached in a different place in the same chromosome - no loss/ gain of genetic material

57
Q

What is a paracentric inversion

A

Both breakpoints are on teh same arm

Doesn’t Invlove the centromere

58
Q

What is haploinsufficneiny

A

How intolerant of a loss of copies that specific gene is =

Low scores = greater likelihood of pathogenicity

59
Q

Why are cytogenetic analysis needed rather than DNA tests sometimes

A

For genome arrangements eg, translocations

Eg, WGS/ array CGH wouldn’t pick up on balanced reciprocal arrangements as no change in ‘amount’ of material

60
Q

What is a balanced reciprocal rearrangement

A

Both chromosomes swap segments
No change in amount of DNA material
So this can only be picked up by detecting that abnormal junction DNA sequence

61
Q

What is a reciprocal translocation

A

Breaks and exchanges - may show no abnormality
Abnormality risk = 5-10%
Reproductive risks
1/ 500 normal individuals

62
Q

What is mietoic quadrivalent / pachytene cross

A

The way the the homologous segments match up/ pair at mieosis (the way they then segregate determines if its a balanced or not segregation)

63
Q

Why is an alternate segregation of the pachytene cross balanced

A

Divides in ‘an opposite cross going away’ so there is an equal amount of each chromosome

64
Q

Why is adjacent segregation unbalanced

A

Divides ‘up and down’ so the there is an unequal number of each chromosome on each divided side

65
Q

What is a Robertsonain translocation

A

Chromosome attaches to teh other, whole arm fusion
Reproductive risk
1/1000 normal
Acrocentric (short arm loss)

66
Q

What do the short arms of ch, 21 and 22 contains

A

No unique genes

RDNA nad satellite repeats

67
Q

What is 47, XX, +21

A

Down’s syndrome

Y2 EMS- Theme 2- Genetic And Environmental Causes Of Disease (7 decks)

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