Session 16-Chromosome Abnormalities Flashcards Preview

Semester 1-MCBG > Session 16-Chromosome Abnormalities > Flashcards

Flashcards in Session 16-Chromosome Abnormalities Deck (40):
1

What is cytogenetics?

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

2

Why do cytogenetic analysis? (4)

1. Accurate diagnosis/prognosis of clinical problems
2. Better clinical management
3. Assess future reproductive risks
4. Prenatal diagnosis

3

How many miscarriages counts as 'recurrent foetal loss'?

3 or more

4

What are the two types of referral reasons?

Constitutional abnormalities
Acquired abnormalities

5

What are the types of constitutional abnormalities? (5)

Prenatal diagnosis
Birth defects
Abnormal sexual development
Infertility
Recurrent foetal loss

6

What are the types of acquired abnormalities? (3)

1. Leukaemias:
Acute disease-AML/ALL (acute myeloid/lymphoblastic leukaemia)
Chronic disease-CML (chronic myeloid leukaemia)
Myelodysplasia/myeloproliferative disorders
2. Solid tumours
3. Specific translocations/abnormalities

7

What are the two main methods of prenatal diagnosis?

1. Chorionic villus sampling-at end of first trimester of pregnancy
2. Amniocentesis-2nd trimester

8

Why do prenatal diagnosis? (5)

1. Maternal serum screening for Down's syndrome-blood sample taken at around 15 weeks, biochemical markers are measured
2. First trimester screening
3. FH chromosome abnormality
4. Abnormal ultrasound scan
5. DNA studies

9

What are some examples of birth defects? (5)

1. Dysmorphism
2. Congenital malformations
3. Mental retardation
4. Development delay
5. Specific syndromes:
Down syndrome (trisomy 21)
Williams syndrome
DiGeorge syndrome

10

What is karyotyping?

Systemic sorting of chromosomes

11

What is aneuploidy?

Loss and gain of whole chromosomes due to errors at cell division in meiosis

12

Give three examples of trisomies

Down Syndrome +21
Patau syndrome +13
Edwards +18

13

Give an example of a monosomy

Turner syndrome 45,X (X inactivation)

14

What is polyploidy?

Gain of a whole haploid set of chromosomes

15

What is the cause of polyploidy?

Polyspermy=fertilisation of an egg by more than one sperm

16

What are the causes of aneuploidy?

Originates from non-disjunction at one of the meiotic cell divisions and forms gametes with a missing chromosome and an extra chromosome

17

True or false: aneuploidy can occur during mitotic cell division

TRUE

18

What does aneuploidy in mitotic cell division cause?

Mosaicism ie two cell populations in an individual

19

What are the characteristics of Down syndrome? (6)

Hypotonia
Characteristic facial features
Intellectual disability
Heart defects
Increased prevalence of leukaemia
Increased incidence of early Alzheimer's

20

What are some of the signs of Edwards syndrome? (4)

Small lower jaw
Low-set ears
Rocker bottom feet
Overlapping fingers

21

What is X chromosome inactivation?

Only one X chromosome is ever active in a human cell

22

Why is a single X chromosome a problem?

X and Y chromosomes have short regions in common at the tips of the long and short arms (PAR1 in Y and PAR2 in X) and this allows for pairing during cell division. Turner syndrome patients will be monosomic for genes in the PARs

23

Which gene is associated with short stature?

SHOX (within PAR)

24

What are the signs of Turner syndrome? (6)

Puffy feet
Redundant skin at back of neck
Short stature
Heart defects
Mild learning difficulties
Infertility

25

What is mosaicism?

Presence of two or more cell lines in an individual

26

What are the two types of translocations?

Reciprocal
Robertsonian

27

What are the different types of cytogenetic structural abnormalities? (8)

Translocations
Inversions
Deletions
Duplications
Insertions
Rings
Marker chromosomes
Isochromosomes

28

What are isochromosomes?

Mirror image chromosomes

29

What are the two types of inversions?

Paracentric
Pericentric

30

What are reciprocal translocations?

Two break rearrangements - exchange of material between nonhomologous chromosomes

31

What are the types of mal-segregation in meiosis?

Adjacent 1-non homologous centromeres move together to daughter cell
Adjacent 2-homologous centromeres
3:1 non disjunction
4:0 non disjunction

32

What does FISH stand for and what is it?

Fluorescent in situ hybridisation
Molecular cytogenetic technique

33

What are the different types of FISH probes? (4)

1. Locus/gene specific probes
2. Centromere probes
3. Telomere probes
4. Whole chromosome paints

34

What are centromere probes used for and what are their characteristics?

Large probes, easy to see metaphase and interphase
Used for: identifying derivative chromosomes and markers

35

What are whole chromosome paints used for?

To identify individual chromosomes even when they are rearranged

36

What are locus specific probes used for?

Microdeletion/duplication syndromes

37

What does microarray comparative genomic hybridisation (aCGH) examine?

Whole genome at high resolution

38

What are the advantages of aCGH? (5)

1. Examines entire genome and high resolution
2. Targeted against known genetic conditions
3. One array is equivalent of many FISH investigations
4. Detailed info on genes in del/dup region
5. Better phenotype/genotype correlation

39

What are the disadvantages of aCGH? (4)

1. Arrays more expensive than karyotyping
2. Won't detect balanced rearrangements
3. Copy number variation
4. Mosaicism may be missed

40

What is copy number variation?

Sections of genome are repeated and number of repeats in genome vary between individuals