Genetic Variation and Disease I

Question 1

What can help to recognise a chromosome?

Answer 1

Length, position of centromere and banding pattern with specific stains

Question 2

What are the structures of a chromosome?

Answer 2

Telomere, short arm (p), centromere, long arm (q), telomere

Question 3

What is different about acrocentric chromosomes?

Answer 3

The short arm doesn’t matter - satellite ribosomal genes, tRNAs etc

Question 4

What is a balanced chromosome rearrangement?

Answer 4

All the chromosomal material is present

Question 5

What is an unbalanced chromosome rearrangement?

Answer 5

Extra or missing chromosomal material, usually 1 or 3 copies of the genome rather than 2

Question 6

What is aneuploidy?

Answer 6

Whole extra or missing chromosome

Question 7

What is translocation?

Answer 7

Rearrangement of chromosomes, ie sections of different chromosomes switched out

Question 8

What are insertions/ deletions?

Answer 8

Missing or duplicated genetic material

Question 9

What is Robertsonian translocation?

Answer 9

Two acrocentric chromosomes stuck end to end. An increased risk of trisomy in pregnancy

Question 10

Why is X chromosome aneuploidy better tolerated?

Answer 10

X inactivation

Question 11

What is reciprocal translocation?

Answer 11

When the translocation occurs over two chromosomes from different pairs

Question 12

What are the reproductive risks of reciprocal translocation?

Answer 12

50% will have normal chromosomes or the translocation will be balanced. Unbalanced (50%) products mainly result in miscarriage or sometimes dysmorphic delayed child.

Question 13

What are the pros and cons or molecular cytogenetics?

Answer 13

You don’t need to see chromosomes to count them - quick, cheaper and more sensitive. However, you will only detect imbalance, and can detect tiny changes - some of which are polymorphisms

Question 14

What is Array CGH?

Answer 14

DNA based technique that is genomewide and also finds lots of polymorphisms. Can detect any size of imbalance but does not detect balanced rearrangements

Question 15

Where do New mutations occur?

Answer 15

In gametogenesis

Question 16

What is mosaicism?

Answer 16

One human who has different cells with different genetic constitution.

Question 17

Where does somatic mosaicism exist?

Answer 17

At meiosis and mitosis - for one chromosomal abnormality is one genetic change that contributes to cancer)

Question 18

What could chromosome changes lead to?

Answer 18

Oncogene activation or deletion of a tumour supressor (stops cell division from being able to continue)

Question 19

What does PCR allow?

Answer 19

The selection of one small piece of the human genome (100-10,000 bases) and amplify it

Question 20

What does Next Generation Sequencing allow?

Answer 20

A whole genome to be sequenced (in a day) or the sequencing of all known exons - all quite cheaply!

Question 21

If only a small section of the genome is exons, what does the rest do?

Answer 21

Regulation of genes, spaces genes out (insulates genes from promotors) and provides substrate to expand genome (add genes)