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

5. Chromosomal Pathology Flashcards

(67 cards)

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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
What happens in sex chromosome aneuploidy in regards to X inactivation
One X chromosome is inactivated cos of dosage compensation
26
What is the Karyotype for Turner Syndrome (sex ch. aneuploidy)
45, X (only one X chromosome)
27
Does Turner syndrome affect males and females
Females
28
Symptoms of Turner Syndrome
``` Short stature Infertility - primary ammenorrhea = absence of menstruation Foetal/ neonatal oedema Neck webbing Aortic coarctation 1/2500 ```
29
Chromosomes in Klinfelter syndrome
47, XXY (males born with extra X chromosome)
30
Does klinfelter syndrome affect males or females
Males
31
Symptom of klinfleter syndrome
Male infertility
32
Polyploidy meaning
Whole extra haploid set of 23 chromosomes
33
Give two examples of when polyploidy is seen
Cancer cells Abnormal conception in pregnancy (Errors at fertilisation, extra chromosomes can be paternal or maternal)
34
What percentage of all pregnancies does polyploidy occur in
2%
35
What is digyny
When an unreduced maternal gamete (2n, sister chromatids haven’t separated properly) fertilises a reduced (normal, haploid) paternal gamete = maternal extra chromosome
36
Symptoms of digyny
Growth retardati on in foetus and placenta and more
37
What is dispermy
Extra paternal chromosomes | 2n from father but normal n from mother
38
Deletion meaning
Loss of chromosome segments
39
Duplicate meaning
Gaining extra chromosome material
40
Mosaicism meaning
Two or more cell populations with a different genotype exists in an organism
41
What is FISH and what is it sued for
Fluorescent in situ hybridisation | - can visualise and map the genetic material in cells, including specific genes or portions of genes
42
How does FISH work
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
What is G-banding used for
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
What is whole genome sequencing
Method for analysing entire genomes
45
Advantages of WGS
- 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
What kinds of things can WGS detect
Single nucleotide variants, insertions/ deletions, CNV, large structural variants
47
What is chromosomal microarray
Looks for CNVs: Duplications and deletions ( eg, trisomy such as Down’s syndrome, monosomy)
48
How does microarray work
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
What is QF- PCR
Quantitative Fluorescent PCR is a molecular test for the identification of common aneuploidy syndromes: 13, 18, 21
50
How does QF- PCR work
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
What test can be used to test for DiGeorge syndrome
FISH as it can detect micro deletion | (DiGeorge syndrome has 2- Mb deletion of chromosome 22q11.2
52
Does fish or g banding have higher resolution
Fish
53
What is a novel junction
Place where the extra genetic material meets the existing one in duplication of a gene
54
Which molecular test is important for during pregnancy
QF PCR
55
What is a pericentric inversion
If both breakpoints are on different arms | ‘Around the centromere’
56
Inversion meaning
When DNA breaks away and attached in a different place in the same chromosome - no loss/ gain of genetic material
57
What is a paracentric inversion
Both breakpoints are on teh same arm | Doesn’t Invlove the centromere
58
What is haploinsufficneiny
How intolerant of a loss of copies that specific gene is = | Low scores = greater likelihood of pathogenicity
59
Why are cytogenetic analysis needed rather than DNA tests sometimes
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
What is a balanced reciprocal rearrangement
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
What is a reciprocal translocation
Breaks and exchanges - may show no abnormality Abnormality risk = 5-10% Reproductive risks 1/ 500 normal individuals
62
What is mietoic quadrivalent / pachytene cross
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
Why is an alternate segregation of the pachytene cross balanced
Divides in ‘an opposite cross going away’ so there is an equal amount of each chromosome
64
Why is adjacent segregation unbalanced
Divides ‘up and down’ so the there is an unequal number of each chromosome on each divided side
65
What is a Robertsonain translocation
Chromosome attaches to teh other, whole arm fusion Reproductive risk 1/1000 normal Acrocentric (short arm loss)
66
What do the short arms of ch, 21 and 22 contains
No unique genes | RDNA nad satellite repeats
67
What is 47, XX, +21
Down’s syndrome

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

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