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Flashcards in Chromosomal Abnormalities Deck (45):
1

What is Cytogenetics?

Study of genetic constitution of cells through the visualisation and analysis of chromosomes

2

Why do cytogenetic analysis?

Accurate diagnosis, better clinical management, assess future reproductive risks, prenatal diagnosis

3

Why might you be referred for cytogenetics?

Constiutional abnormalities, prenatal disagnosis, birth defects, abnormal sexual development, infertility, recurrent fetal loss, leukaemia, solid tumours, specific translocations/abnormalities

4

What are the two types of prenatal diagnosis?

Chorionic villus and Amniocentesis

5

What can be seen in prenatal diagnosis?

Maternal screening for down syndrome, first trimester screening, FH chromosome abnormality, Abnormal ultrasound scan, DNA studies

6

What birth defects can be seen on prenatal scan?

Dysmorphism, congenital malformations, mental retardation, developmental delay, specific syndromes like down, williams and digeorge syndrome,

7

At what stage are chromosomes karyotypes?

Metaphase

8

How do you analyse chromosomes?

Count the number of chromosomes, identify each chromosome pair, assess if there is any missing or extra material,must be seen at correct resolution twice and be independently rechecked once

9

How do you describe a karyotype?

chromosome number, sex complement and structural changes, separated by commas e.g. 46, XX- normal female

10

What are Trisomies?

Extra chromosome e.g. down syndrome

11

What are monosomies?

Less chromosomes e.g. turner syndrome

12

What is polyploidy?

Gain of a whole haploid set of chromosomes

13

What causes polyploidy?

polyspermy- when an egg is fertilised by more than one sperm

14

What is anaphase lag?

Chromosomes left behind and not pulled to poles

15

What are the symptoms of down syndrome?

Hyptonia, characteristic, facial features, heart defects, increased chance of leukaemia, alzeimers

16

Which chromosome is trisomy in down syndrome?

21

17

What chromosome is trisomy in Edwards syndrome?

18

18

What are the symptoms of Edwards Syndrome?

Small lower jaw, prominent occiput, low-set ears, rocker bottom feet, overlapping fingers, live 5-15 days

19

What chromosome is Trisomy in Patau syndrome?

13

20

What is X chromosome inactivation?

One X chromosome is ever active in a human cell

21

Why does Turners syndrome occur?

Monosonic for genes in the Par regions

22

What are the symptoms of Turners syndrome?

Puffy feet, redundant skin at back of neck, short, heart defects, mild learning difficulties, neck webbing, infertile

23

What is Mosaicism?

Presence of two or more cell lines in an individual

24

What usually causes mosaicism?

Mitotic non-disjunction

25

What is a reciprocal translocation?

Two break arrangement, carriers will produce balanced and unbalanced gametes, will have abnormal phenotype if unbalanced

26

What are the types of secregation in Meiosis?

Alternate- balanced
Adjacent 1- non homologous centromeres
Adjacent 2- homologous centromeres
3:1 non disjunction
4:0 non disjunction

27

How do you assess unbalanced segregation outcomes?

Establish the likely segregation, see if the imbalances have been reported before, quote risk if established

28

What is a robertsonian translocation?

Two afrocentric chromosomes fused together- carrier is phenotypically normal but child will not be

29

When does prenatal aneuploidy screening take place?

Interphase

30

What occurs in prenatal aneuploidy screening?

14 days in culture which causes anxiety, FISH

31

What can microarray not detect?

Balanced rearrangments

32

Who would be referred for a microarray?

learning difficulties, normal karyotype to see if its really balanced and unbalanced karyotypes to assess gene control

33

What are the positives of microarray?

examines whole genome at a high resolution, targeted against known genetic conditions, equivalent to 1000s of fish investigations, detailed info on del/dup regions, better phenotype and genotype correlation

34

What are the negatives of microarray?

more expensive than karyotyping, do not detect balanced rearrangements, masaicism may be missed, copy number variation

35

How do deletions and duplications arise?

Uneven pairing and recombination during meiosis

36

How would you report abnormal chromosome results?

Give the ISCN
Describe abnormality in works and what it means, relate to clinical problem, request family samples if requires, refer to clinical genetics, provide appropriate literature

37

What is Uniparental disomy?

Homologous chromosomes from one parent

38

Why is UPD a problem?

Imprinting

39

What syndromes are caused by UPD?

Prader-willi, Russell-Silver and Beckwith-Wiedemann

40

How does UPD occur?

Trisomy rescue, monosomy rescue, gamete complementation, mitotic error

41

What is NGS?

Next generation sequencing- sequence fragments in parallel, reveals entire genomes DNA

42

What are the positive of NGS?

Increased read length, high throughput, automated workflow, simplified protocols

43

What are the negatives of NGS?

Whole genome sequencing costs high, insufficient IT capacity, lack of knowledge to fully interpret findings, ethically

44

How is non-invasive prenatal testing done?

Uses cell free metal DNA in maternal plasma

45

What are liquid biopsies used for?

Non invasive cancer testing