L16: Chromosomal Mutations

Question 1

What is a chromosome?

Answer 1

Threadlike structure of nucleic acid & protein found in the nucleus, carrying genetic information in the form of genes

Question 2

Main components of the chromosome

Answer 2

1) Chromosome arms: short (p) & long (q) arms
2) Centromere
3) Kinetochore
4) Telomeres
5) Subtelomeres

Question 3

What is kinetochore?

Answer 3

Protein complex at centromere where spindle fibres attach

Question 4

What is a centromere?

Answer 4

link sister chromatids

Question 5

Features of centromere

Answer 5

Multiple repeating sequences

Question 6

What are telomeres?

Answer 6

Specialised repeated DNA sequences
Protect ends of chromosomes

Question 7

What are subtelomeres?

Answer 7

Chromosome part between gene-rich areas & telomeres

Question 8

Describe metacentric chromosome

Answer 8

centromere in the middle
telomere at the top
p & q arm

Question 9

4 chromosome classification based on centromere position

Answer 9

1) Telocentric: centromere at end
2) Metacentric: centromere in the middle
3) Submetacentric: Centromere slightly off-center
4) Acrocentric: Centromere close to 1 end

Question 10

What is cytogenetics the study of?

Answer 10

Chromosome variations & their link to traits/illnesses

Question 11

How do cytogeneticists distinguish chromosome types by size & shape?

Answer 11

Use stains to contrast dark heterochromatic (repetitive DNA sequences) with lighter euchromatin (more protein encoding gene)

Question 12

What is a karyotype?

Answer 12

An individual’s collection of chromosomes

Question 13

What is karyotyping?

Answer 13

Process of pairing & ordering all chromosomes of an organism

Question 14

Karyotype of a normal female & male

Answer 14

Female: 46, XX
Male: 46, XY

Question 15

What is the G banding technnique?

Answer 15

Uses giemsa dye to stain chromosomes, highlighting euchromatin (light bands) & heterchromatin (dark bands)

Question 16

How is chromosome nomenclature organised?

Answer 16

1st number/letter represent chromosome

2nd letter p/q describes arm

Then region/band number

Question 17

What is Fluorescence In Situ Hybridisation (FISH)?

Answer 17

Uses fluorescent DNA probes to detect specific chromosomal abnormalities

Question 18

How many fluorescently labelled DNA probes are used to analyse location in FISH?

Answer 18

2

Question 19

What is the purpose of the 2 fluorescently labelled DNA probes in FISH?

Answer 19

1st probe: Control & hybridises with DNA on target chromosome (outside targeted region)

2nd probe: Hybridises to a target location on individual’s DNA sequence

Question 20

What is chromosome painting?

Answer 20

Form of FISH where multiple probes label different chromsome regions

Question 21

Procedure of FISH

Answer 21

1) Chromosomes fixed on a slide & denatured
2) Fluorescent probes hybridise to complementary sequences
3) Analysis under fluorescence micrscope

Question 22

Constitutive vs acquired chromosome abnormalities

Answer 22

Constitutive: all the tissues hold the same anomaly

Acquired: only 1 organ is involvedm all others are normal

Question 23

Homogeneous vs Mosaic chromosome abnormalities

Answer 23

Homogeneous: all cells (studied) carry anomaly

Mosaic: only some cells carry anomaly (cancer cells)

Question 24

Numerical vs Structural chromosome abnormalities

Answer 24

Numerical: total no. of chromosomes in humans is not 46

Structural: defects including missing, extra genetic material within a chromosome

Question 25

3 types of numerical chromosomal abnormalities

Answer 25

1) Euploidy 2) Polypoidy 3) Aneuploidy

Question 26

What is euploidy?

Answer 26

Normal no. & sets of chromosomes

Question 27

What is polypoidy?

Answer 27

Presence of 3 or more complete sets of chromosomes

Question 28

What is aneuploidy?

Answer 28

Presence of additional/missing individual chromosomes

Question 29

2 types of structural abnormalities

Answer 29

1) balanced chromosomal rearrangments 2) unbalanced rearrangments

Question 30

What is balanced chromosmomal arrangments?

Answer 30

Type of chromosomal structural involving chromosmal rearrangements with gain/loss of chromatin

Question 31

What is unbalanced rearrangements?

Answer 31

Include deletions, duplications of a chromosome segment when there is additional/missing genetic information

Question 32

2 types of polypoidy

Answer 32

triploidy: 3 sets of chromosomes (23x3=69) tetraploidy: 4 sets of chromosomes (23x4=92)

Question 33

3 types of aneuploidy

Answer 33

1) monosomy: 1 less chromosome (23x2)-1=45 2) trisomy: 1 additional chromosome (23x2)+1=47 3) nullisomy: pair of homologous chromosome is missing (22x2=44)

Question 34

Define nondisjunction

Answer 34

Failure of homologous chromosomes/sister chromatids to separate

Question 35

What is autosomal aneuploidy?

Answer 35

All abnormalities that DO NOT involve sex chromosomes

Question 36

What is sex chromosome aneuploidies?

Answer 36

All abnormalities that INVOLVE sex chromosomes

Question 37

Karyotype of down syndrome

Answer 37

47, XY, +21

Question 38

Karyotype of turner syndrome

Answer 38

45,X

Question 39

Karyotype of Klinefelter Syndrome

Answer 39

47, XXY

Question 40

4 type of structural chromosome abnormalities

Answer 40

deletion, duplication, inversion, translocation

Question 41

What is submicroscopic deletions?

Answer 41

Too small to be detected by light microscopy

Question 42

2 types of translocation in structural abnormalities

Answer 42

Reciprocal: segments from 2 different chromosomes have been exchanged Robertsonian: entire chromosomal arm has been attached to another at/close to centromere

Question 43

What is translocation?

Answer 43

Portion of 1 chromosome is transferred to another chromosome

Question 44

What is inversion?

Answer 44

Portion of chromosome broken off, turned upside down, reattached, genetic material is inverted

Question 45

2 types of inversions

Answer 45

Paracentric inversion: not including centromere Pericentric inversion: INCLUDES centromere

Question 46

What is a ring chromosome abnormality?

Answer 46

A portion of a chromosome has broken off & formed a circle/ring, as ends fuse together

Question 47

What are isochromosomes abnormalities?

Answer 47

Formed by a mirror image copy of a chromosome segment including the centromere

Question 48

What is uniparental disomy?

Answer 48

Both copies of a chromosome inherited from 1 parent

Question 49

2 examples of uniparental disomy

Answer 49

Angelman Syndrome: maternal chromosome deletion Prader-Willi Syndrome: paternal chromosome deletion

Question 50

What are trinucleotide repeats?

Answer 50

Expansion of 3-nucleotide DNA sequences, leading to disorders - cause dynamic/unstable mutation

Question 51

Examples of trinucleotide repeats

Answer 51

1) Fragile X Syndrome: CGG repeat 2) Huntington's Disease: CAG repeat

Question 52

What genetic disorders does DNA repair defects lead to?

Answer 52

Xeroderma Pigmentosum (UV, skin cancer) Werner Syndrome: premature aging Fanconi Anemia: Bone marrow failure

Question 53

What is a transposable element?

Answer 53

DNA sequence that can change its position within a genome

Question 54

What is synteny?

Answer 54

Conservation of the relative order of genes/genetic markers across different species genomes