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POM 5: Genetics > 4: Chromosomal abnormalities > Flashcards

4: Chromosomal abnormalities Flashcards

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1
Q

p

A

short arm

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2
Q

q

A

long arm

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3
Q

pter

A

tip of short arm

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4
Q

qter

A

tip of long arm

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5
Q

cen

A

centromere

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6
Q

del

A

deletion

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7
Q

der

A

derivative chromosome (contains extra material)

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8
Q

dup

A

duplication

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9
Q

ins

A

insertion

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10
Q

inv

A

inversion

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11
Q

t

A

translocation

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12
Q

+/- before chromosome number

A

gain/loss whole chromosome

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13
Q

+/- after chromosome number

A

gain/loss part of chromosome

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14
Q

Preparation and staining of karyotypes

A

collect ~5ml heparinised venous blood (amniotic cells, CVS)
Isolate white cells
culture in presence of phytohemagglutinin (stimulates T-lymphocyte growth/differentiation)
after 48h, add colchicine - mitotic arrest in metaphase
place in hypotonic saline
place on slide
fix and stain

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15
Q

what stain is used for investigating karyotypes

A

Giemsa stain
- often done in prophase than metaphase

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16
Q

Architecture of karyotypes and causes

A

G-banded architecture
caused by different staining on chromosomes
Sub-bands develop with increasing resolution- help identify smaller abberations as looking at smaller sections of chromosomes

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17
Q

BHP

A

bands her haploid set

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18
Q

What do the bands on a karyotype show

A

Show how much stain has been taken up in that part of the chromosomes

Dark - heterochromatin - more compact, fewer genes
Light - euchromatin - more open, more genes

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19
Q

Two types of chromosomal abnormalities

A

Chromosome number
Chromosome structure

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20
Q

2 abnormalities involving chromosome number

A

Aneuploidy
Mosaicism

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21
Q

6 abnormalities involving chromosome structure

A

crossing over
single chromosomal abnormalities
two chromosome abnormalities
deletions
duplications
Robertsonian translocation

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22
Q

Aneuploidy is

A

abnormal number of chromosomes (not divisible by 23)
can be :
trisomy - too much (most not compatible with life)
monosomy- insufficient (poorly tolerated)

23
Q

Cause of Aneuploidy

A

Non-disjunction (uneven number from meiosis)
can happen in meiosis 1 or 2

24
Q

If non-disjunction arises from Meiosis I

A

All daughter cells affected (4)

25
Q

If non-disjunction arises from Meiosis II

A

Half daughter cells affected (2)

26
Q

What does non-disjunction result in

A

either +1 or -1 chromosome in each gamete
when fertilised results in trisomy/monsomy

27
Q

Meiosis is

A

division of cells to produce haploid gametes
divide twice - ensures genetic variation in gametes by random assortment of monologues and recombination

28
Q

What is the most common form of aneuploidy

A

Sex chromosome aneuploidy - tolerated

29
Q

What is the incidence of sex chromosome aneuploidy

A

1 in 400 in males
1 in 650 in females

30
Q

How is sex chromosome aneuploidy tolerated (2)

A

X-inactivation of excess X chromosomes
Low gene content of Y chromosomes

31
Q

Why does sex chromosome aneuploidy still have an effect on the person

A

Both X and Y chromosome have PAR - pseudo autosomal region and always active

32
Q

Down syndrome arises in

A

maternal non-disjunction 47 +21/ 47,XX +21
trisomy 21

33
Q

What factors contribute to increased risk of down syndrome (maternal)

A

-Incr. in maternal age as incr. risk of maternal non-disjunction
caused by oogenesis venerability -oocytes arrested in prophase I until puberty, then metaphase II until fertilisation
- homologous chromatids held by factors - overtime proteins break down, causing random chromatid separation

34
Q

Paternal contribution to aneuploidy

A

age Not risk factor for aneuploidy
Affects subset of single gene disorders - selfish spermatogonial selection - selective advantage of mutant cells over neighbouring wild cells
-smoking is a risk factor

35
Q

Mosaicism is

A

presence of 2(+) populations of cells with different genotypes

36
Q

Two mechanisms of mosaicism

A

non-disjunction during early development
loss of extra chromosomes in early development

37
Q

Crossing over occurs in

A

prophase I

38
Q

Purpose of crossing over

A

increases genetic diversity

39
Q

Process of crossing over

A

Pairs of chromosomes align, chiasma form and crossover occurs
1-3 x per chromosome per meiosis

40
Q

What can go wrong in crossing over of chromosomes

A

chromosomes not lined up, incorrect sections cross

41
Q

3 types of single chromosome abnormalities

A

Deletion - unequal crossing over or breakage of chromosome ends and incorrect re-joining of broken ends
Duplication - only caused by unequal crossing over
Inversion - breaks in arms are inverted and reinserted into chromosome

42
Q

Two examples of two chromosome abnormalities

A

Insertion - section of chromosomes inserted into another
Translocation - exchange of material
-may not affect carrier - can affect offspring, causing partial trisomy or monosomy e.g Cri-du-chat syndrome

43
Q

Example of a chromosomal abnormality caused by deletions

A

Williams syndrome

44
Q

Two types of inversions

A

Paracentric - distant from centromere
Pericentric - break around centromere

45
Q

Types of deletions

A

Microscopic - easily detected on microscope
Microdeletion - seen in v high resolution banding: molecular genetics (20+ genes deleted0

46
Q

What is the chromosomal configuration of Cri-du-chat syndrome

A

46,XY,del(5p)

47
Q

What is the chromosomal configuration of Williams syndrome

A

7q11.23 deletion

48
Q

Symptoms of Williams syndrome

A

Long philtrum
Short, upturned nose
arched eyebrows
Supravalvular aortic stenosis
friendly, social personality

49
Q

What is the deletion in williams syndrome detected by

A

FISH (flourescent in situ hybridisation)
too small to be detected by karyotyping

50
Q

7q11.23duplication syndrome is

A

milder phenotype compared to corresponding deletion

51
Q

Symptoms of 7q11.23 duplication syndrome

A

delayed speech development
autistic behaviours affecting communication and social interaction
dilation of aorta
flat eyebrows
broad nose and short philtrum

52
Q

3 classes of chromosomes in robertsonian translocation

A

metacentric - arms same length
submetacentric - (considerably) shorter p arms
acrocentric - just stalk of DNA - short arm reduced to vestibule of DNA

53
Q

Robertsonsian translocation occurs

A

between acrocentric chromosomes
can be homologous or non-homologous
most common 13and14, 14and15, 14and21

54
Q

Effects of robertsonian translocation

A

affects 1 in 1000 people
most people show no affects
can cause problems in offspring

POM 5: Genetics (7 decks)

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