Chromosomal abnormalities

Question 1

How do you analyse chromosomes?

Answer 1

Using a metaphase spread= fix chromosomes on slide & stain them
Karyotype picture produced and can identify chromosome banding

Question 2

What should each chromosome contain?

Answer 2

P arm, Q arm and centromere

Question 3

How do scientists identify chromosomes?

Answer 3

1- Size
2- Banding pattern
3- Centromere position

Question 4

What are acrocentric chromosomes?

Answer 4

Centromere is located very near the top of the chromosome so only the q arm (very little/ no p arm)

Question 5

What is a normal female karyotype?

Answer 5

22 pairs XX

Question 6

What is a normal male karyotype?

Answer 6

22 pairs XY

Question 7

What abnormalities can be picked up on a karyotype?

Answer 7

• Abnormal chromosome number
• Abnormal chromosome material location
• Abnormal amounts of chromosome material (bits missing or extra)

Question 8

What are the 3 main types of chromosomal abnormalities?

Answer 8

Aneuploidies
Microdeletions
Translocations

Question 9

What is aneuploidy?

Answer 9

Abnormal number of copies of an individual chromosome

Question 10

What is Monosomy?

Answer 10

1 chromosome missing, Total= 45

Question 11

What is Trisomy?

Answer 11

1 chromosome extra, Total= 47

Question 12

What is polyploidy?

Answer 12

Abnormal number of sets of chromosomes

Question 13

What is Monoploid?

Answer 13

One set, Total= 23 pairs

Question 14

What is Diploid?

Answer 14

Two sets, Total= 46 pairs

Question 15

What is Triploid?

Answer 15

Three sets, Total= 69 pairs

Question 16

What are deletions?

Answer 16

Loss of a segment of genetic material from a chromosome

Question 17

What are duplications?

Answer 17

Gain of a segment of genetic material from a chromosome

Question 18

What are microdeletions/ microduplications?

Answer 18

too small to be seen on a karyotype

Question 19

What is the consequence of deletions & duplications?

Answer 19

depends on which genes are in the deleted/ duplicated region

Question 20

What is a translocation?

Answer 20

Relocation of chromosome material to the wrong place

Question 21

What is a reciprocal translocation?

Answer 21

2 different chromosomes have exchanged segments with each other

Question 22

What is a Robertsonian translocation?

Answer 22

An entire acrocentric chromosome attaches to another at the centromere

Question 23

What is a balanced translocation?

Answer 23

All chromosome material present (just in the wrong place)

Question 24

What is an unbalanced translocation?

Answer 24

Relocation has resulted in loss and/ or gain of chromosome material

Question 25

What is down syndrome?

Answer 25

Trisomy 21 (3 copies of chromosome 21)

Question 26

What are the 6 clinical features of Down's syndrome?

Answer 26

- Characteristic facial features - Mild= moderate intellectual disability - Short stature - Congenital heart disease - Endocrine problems - Increased risk of leukaemia and Alzheimer's

Question 27

What are 10 phenotypic changes associated with Down's syndrome?

Answer 27

- Up-slanting palpebral fissues - Prominent epicanthic folds - Flat nasal bridge/ flat facial profile - Low set small ears - Furrowed tongue - Single transverse palmer crease - Clinodactyly - Brushfield spots - Sandal- toe deformity - Excess nuchal skin

Question 28

What is Edward's Syndrome?

Answer 28

trisomy 18

Question 29

What are the 6 clinical features of Edward's syndrome?

Answer 29

- Intra-uterine growth restriction - Most die during pregnancy/ neonatal period - Overlapping fingers - Rocker-bottom feet - Congenital heart/kidney disease - Small head size (microcephaly)

Question 30

What is Patau's syndrome?

Answer 30

Trisomy 13

Question 31

What are 6 clinical features of Patau's syndrome?

Answer 31

- Intra-uterine growth restriction - Most die during pregnancy/ neonatal period - Cleft lip/ palate - Extra fingers/ toes - Brain abnormalities - Congenital heart disease

Question 32

What is Antenatal combined screening?

Answer 32

Combined scan for down's syndrome, edwards syndrome and pataus syndrome, done via blood test & ultrasound scan

Question 33

What is Klinefelter syndrome?

Answer 33

47 XXY

Question 34

What are 4 clinical features of Klinefelters syndrome?

Answer 34

- Tall stature - Normal intellect - Infertile- often diagnosed in a fertility clinic - Little facial/ body hair

Question 35

What is Turner syndrome?

Answer 35

Monosomy X (45, XO)

Question 36

What are the 7 clinical features of Turner syndrome?

Answer 36

- Infertility - Short stature - Lymphoedema (puffy hands and feet) - Webbed neck - Endocrine abnormalities - Congenital heart disease - Normal intellect

Question 37

What is Di George syndrome?

Answer 37

22q11.2 microdeletion

Question 38

What are 6 clinical features of Di George syndrome?

Answer 38

- Congenital heart and Kidney disease - Nasal speech - Characteristic facial features - Hypocalcaemia - Intellectual disability (mild- severe) - Increased risk of psychiatric disorders

Question 39

What is Prader Willi syndrome?

Answer 39

15q11.2-q13 microdeletion most common mechanism

Question 40

What are 6 clinical features of Prader Willi syndrome?

Answer 40

- Low tone at birth - Short stature - Characteristic facial features - Challenging behaviours + hyperphagia - Intellectual disability - Absent/ incomplete pubertal development

Question 41

How is Chronic myeloid leukaemia caused?

Answer 41

- Reciprical translocation between chromosomes 9 and 22 resulting in the Philadelphia chromosome -BCR gene from chromosome 22 fuses with ABL gene from chr9 creating a fusion oncogene called BCR::ABL

Question 42

What does BCR::ABL do?

Answer 42

- Directs production of mutant protein which drives conversion of normal bone marrow stem cells into leukaemic cells

Question 43

What are balanced reciprocal translocations associated with?

Answer 43

Recurrent miscarriage and multiple congenital anomalies

Question 44

What do robertsonian translocations involving chromosome 21 cause?

Answer 44

Recurrent miscarriage and recurrent down syndrome