2. Cytogenetics

Question 1

Cytogenetics

Answer 1

The study of chromosome number, structure and function

Question 2

Chromsome territory model

Answer 2

If chromosomes occupied distinct territories, localised damage would affect only a small subset of chromosomes

Question 3

Random organisation model

Answer 3

If the chromatin fibres of each chromosome were randomly distributed throughout the nucleus many chromosomes would be damaged

Question 4

Structural chromosome defects grouped on the basis of..

Answer 4

• Number of chromosome breakages

- Number of chromosomes involved

Question 5

Deletions: What is it and what is the result

Answer 5

• Occurs when a chromosome breaks and a piece is lost

- Results in partial monosomy for that chromosome

Question 6

Types of deletions

Answer 6

Terminal and interstitial

Question 7

Example of disease where terminal deletion has occurred

Answer 7

Cri-du-chat (5p-), partial deletion of short arm on chromosome 5

Question 8

Example of disease where interstitial deletion has occurred

Answer 8

Williams syndrome, deletion of elastin genes on long arm of chromosome 7

Question 9

Translocation

Answer 9

Chromosome break and the fragments rejoin to other chromosomes

Question 10

Loss of genetic material during translocation?

Answer 10

No, but breakpoint can disrupt a critical gene or juxtapose pieces of two genes to create a fusion gene

Question 11

Translocations cause reductions in fertility?

Answer 11

Yes

Question 12

Types of translocations

Answer 12

Reciprocal, Robertsonian (centric fusion), insertional

Question 13

Reciprocal translocation

Answer 13

Exchange of material between nonhomologous chromosomes

Question 14

Robertsonian translocation

Answer 14

Takes place between acrocentric chromosomes,. Break takes place at or near centromere

Question 15

Inversion

Answer 15

Occur after a breakage -> chromosome fragment is inverted and rejoined (not lost!)

Question 16

Types of inversions

Answer 16

• Paracentric (centromere. not involved)

- Pericentric (centromere involved)

Question 17

Insertion

Answer 17

Insertion of one part of a chromosome into another chromosome

Question 18

Ring chromosome

Answer 18

A break removes both telomeres, repaired by creating a ring

Question 19

Isochromosomes

Answer 19

Split the wrong way in mitosis or meiosis 2: The chromosome consists of two copies of either the long (q) arm or the short (p) arm.

Question 20

Prognosis of isochromosome

Answer 20

Poor, except for iXq (isochromosome of the long arm of the X)

Question 21

Euploidy

Answer 21

Normal number of structurally normal chromosomes

Question 22

Aneuploidy

Answer 22

Less or more than normal diploid number

Question 23

Monosomy

Answer 23

Lack of one pair of chromosomes

Question 24

Trisomy

Answer 24

A specific instance of polysomy (3 of a certain chromosome)

Question 25

Trisomy 21

Answer 25

Downs syndrome

Question 26

Trisomy 13

Answer 26

Patau syndrome

Question 27

Trisomy 18

Answer 27

Edwards syndrome

Question 28

Triploidy

Answer 28

Three of every chromosome | 69 human chrs

Question 29

Why does triploidy occur?

Answer 29

- Fertilisation by 2 sperms - Fertilisation by a diploid sperm - Fertilisation of a diploid ovum

Question 30

Only one sex chromosome: X

Answer 30

Turner syndrome

Question 31

Chromosomes XXY

Answer 31

Klinefelter syndrome

Question 32

Chromosomes XYY

Answer 32

Jacobs syndrome

Question 33

Uniparental disomy

Answer 33

When a person receives two copies of a chromosome, or of part of a chromosome, from one parent and no copy from the other parent.

Question 34

Mosaic

Answer 34

An individual with more than one cytogenetically distinct population of cells with the same origin

Question 35

In pregnancy; microchimerism

Answer 35

The presence of a small number of cells that originates from another individual and are therefore genetically distinct from the cells of the host individual

Question 36

How frequent are chromosomal abnormalities?

Answer 36

1/200 newborn children