Genetic Variation and Disease II. Whole Chromosomes to Single Bases

Question 1

Genome structure

Answer 1

Single bases –> DNA strand –> Whole chromosome

Question 2

Chromosome Notation (__XY/XX)

Answer 2

46XX
- Total number of chromosomes
- Sex chromosome complement

Question 3

How a Chromosome is recognised

Answer 3

Telomere - protective cap
Short arm (p)
Centromere
Long arm (q)
Telomere

Question 4

Acrocentric Chromosomes

Answer 4

Centromere not central
Near end of chromosome

Question 5

Balanced Chromosome Rearrangement

Answer 5

All chromosomal material present

Question 6

Unbalanced Chromosome Rearrangement

Answer 6

Extra or missing chromosomal material

Question 7

Aneuploidy

Answer 7

Whole extra or missing chromosome

Question 8

Translocation

Answer 8

Rearrangement of chromosomes

Question 9

Insertions and Deletions

Answer 9

Missing or duplicated material

Question 10

Microdeletions

Answer 10

chromosomal deletions that are too small to be detected by light microscopy using conventional cytogenetic methods

Question 11

Trisomy 21

Answer 11

Gives rise down syndrome

Question 12

Robertsonian Translocation

Answer 12

Two acrocentric chromosomes stuck end to end

Question 13

Balanced Translocation

Answer 13

A type of genetic variant where part of one chromosome has moved, usually to another, non-homologous, chromosome

Question 14

Trisomy 14

Answer 14

Miscarriage

Question 15

Turner Syndrome

Answer 15

45X

Question 16

Triple X

Answer 16

47XXX

Question 17

Klinefelter syndrome

Answer 17

47XXY

Question 18

Reciprocal Translocations

Answer 18

occur due to the exchange of chromosome material between two nonhomologous chromosomes

Reproductive Risks
- Roughly 50% of conceptions will have either normal chromosomes or balanced translocations
-Unbalanced products - miscarriage, dysmorphic delayed child

Question 19

DiGeorge Syndrome

Answer 19

A condition present from birth that can cause a range of lifelong problems, including heart defects and learning difficulties

22q11 deletion

Question 20

Molecular Cytogenetics

Answer 20

No longer need to see chromosomes to count them
You will only detect imbalance
You can detect tiny changes
Some small changes are polymorphisms

Question 21

Where do mutations come from?

Answer 21

Germ line mutation
- One parent has this

New mutation in gametogenesis

One patient is mosaic

Mutation is post-zygotic (child is mosaic)

Question 22

Mosaicism

Answer 22

Different cells have a different genetic constitution

Could be mosaic chromosome abnormality or mosaicism for a point mutation

Question 23

Somatic Mosaicism

Answer 23

Genetic variation that is present in the genomes of cells that make up the body of the organism and do not contribute to gametes produced by the individual

All cells suffer mutations as they divide - meiosis and mitosis
Repair mechanisms exist

Question 24

Chromosome changes could (2)

Answer 24

Activate an oncogene
Delete a tumour supressor

E.g. HER2 amplification and protein expression

Question 25

Philadelphia Chromosome

Answer 25

Bcr-Abl
Chromosome 9 and 22 Translocation
Increased proliferation, decreased apoptosis