lecture 6 - analysis of chromosomal disorders 1

Question 1

What a karyotype, what do the bands represent?

Answer 1

Regions of heterochromatin (less active) or euchromatin (more active) DNA

Question 2

What do the dark bands of a stained chromosome represent?

Answer 2

Inactive DNA - heterochromatin

Question 3

What do the light bands of a stained chromosome represent?

Answer 3

Active DNA - euchromatin

Question 4

What are the 2 classifications of chromosome based on their centromere position?

Answer 4

Acrocentric, metacentric

Question 5

What is an acrocentric chromosome?

Answer 5

Chromosome with the centromere near the end, so has a long and short arm

Question 6

What is a metacentric chromosome?

Answer 6

Chromosome with a central centromere and 2 equally sized arms

Question 7

What is a telomere?

Answer 7

A region of replicated material at the end of the arm of a chromosome

Question 8

What is the name for the long arm of a chromosome?

Answer 8

q arm

Question 9

What is the name for the short arm of a chromosome?

Answer 9

p arm

Question 10

What technique is used to provide a genome-wide survey for imbalances?

Answer 10

Chromosomal microarray

Question 11

What are the clinical indication for assessing chromosomal structure?

Answer 11

Abnormality of growth or development, intellectual disability, recurrent miscarriage, cancer investigation

Question 12

What sex does Turner Syndrome affect?

Answer 12

Girls

Question 13

What are the presentations of Turner Syndrome?

Answer 13

webbed neck, coarction of aorta, growth delay, amenorrhoea, short stature

Question 14

What are the chromosomal causes of Turner Syndrome?

Answer 14

Missing X chromosome or structural abnormality to X chromosome

Question 15

What is mosaic Turner Syndrome?

Answer 15

Abnormality where not all cells in the body are missing an X chromosome

Question 16

Why is Turner Syndrome often mosaic?

Answer 16

Because the loss of an X chromosome is often post-zygotic (not a result of non-disjunction in meiosis) so some cells have X and some don’t

Question 17

Why does Turner Syndrome cause abnormalities when females normally have one X inactivated anyway?

Answer 17

Because the inactivated X chromosome in normal females is only 80% inactivated, and the 20% of genes still expressed are important to normal function

Question 18

Is Turner Syndrome recurrent for mothers?

Answer 18

No

Question 19

What is the karyotype for Turner Syndrome?

Answer 19

45,X

Question 20

What is the karyotype of Klinefelter Syndrome?

Answer 20

47,XXY

Question 21

What are the presentations of Klinefelter Syndrome?

Answer 21

Reduced Testicular function, tall stature, low IQ

Question 22

What is the cause of Klinefelter Syndrome?

Answer 22

Meiotic non-disjunction leading to an extra X chromosome

Question 23

What is chromosomal non-disjunction?

Answer 23

Failure of homologous chromosome to seperate during meiosis 1 or 2

Question 24

What is the karyotype for Down Syndrome?

Answer 24

47,XX,+21 (additional chromosome 21 - trisomy 21)

Question 25

What condition results from trisomy 21?

Answer 25

Down Syndrome

Question 26

What type of translocation occurs in down syndrome?

Answer 26

Robertsonian translocation of Chromosome 21 (centric fusion

Question 27

How can down syndrome be recurrent?

Answer 27

If the parent is a carrier for a robertsonian translocation

Question 28

What is a robertsonian translocation?

Answer 28

When the long arms of 2 chromosomes gets fused together

Question 29

What are reciprocal translocations?

Answer 29

The balanced transfer of material from one chromosome to another

Question 30

What are the signs of reciprocal chromosomal translocations?

Answer 30

Recurrent miscarriage, family history