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POM 5: Genetics > 4: Chromosomal abnormalities > Flashcards

4: Chromosomal abnormalities Flashcards

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
If non-disjunction arises from Meiosis II
Half daughter cells affected (2)
26
What does non-disjunction result in
either +1 or -1 chromosome in each gamete when fertilised results in trisomy/monsomy
27
Meiosis is
division of cells to produce haploid gametes divide twice - ensures genetic variation in gametes by random assortment of monologues and recombination
28
What is the most common form of aneuploidy
Sex chromosome aneuploidy - tolerated
29
What is the incidence of sex chromosome aneuploidy
1 in 400 in males 1 in 650 in females
30
How is sex chromosome aneuploidy tolerated (2)
X-inactivation of excess X chromosomes Low gene content of Y chromosomes
31
Why does sex chromosome aneuploidy still have an effect on the person
Both X and Y chromosome have PAR - pseudo autosomal region and always active
32
Down syndrome arises in
maternal non-disjunction 47 +21/ 47,XX +21 trisomy 21
33
What factors contribute to increased risk of down syndrome (maternal)
-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
Paternal contribution to aneuploidy
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
Mosaicism is
presence of 2(+) populations of cells with different genotypes
36
Two mechanisms of mosaicism
non-disjunction during early development loss of extra chromosomes in early development
37
Crossing over occurs in
prophase I
38
Purpose of crossing over
increases genetic diversity
39
Process of crossing over
Pairs of chromosomes align, chiasma form and crossover occurs 1-3 x per chromosome per meiosis
40
What can go wrong in crossing over of chromosomes
chromosomes not lined up, incorrect sections cross
41
3 types of single chromosome abnormalities
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
Two examples of two chromosome abnormalities
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
Example of a chromosomal abnormality caused by deletions
Williams syndrome
44
Two types of inversions
Paracentric - distant from centromere Pericentric - break around centromere
45
Types of deletions
Microscopic - easily detected on microscope Microdeletion - seen in v high resolution banding: molecular genetics (20+ genes deleted0
46
What is the chromosomal configuration of Cri-du-chat syndrome
46,XY,del(5p)
47
What is the chromosomal configuration of Williams syndrome
7q11.23 deletion
48
Symptoms of Williams syndrome
Long philtrum Short, upturned nose arched eyebrows Supravalvular aortic stenosis friendly, social personality
49
What is the deletion in williams syndrome detected by
FISH (flourescent in situ hybridisation) too small to be detected by karyotyping
50
7q11.23duplication syndrome is
milder phenotype compared to corresponding deletion
51
Symptoms of 7q11.23 duplication syndrome
delayed speech development autistic behaviours affecting communication and social interaction dilation of aorta flat eyebrows broad nose and short philtrum
52
3 classes of chromosomes in robertsonian translocation
metacentric - arms same length submetacentric - (considerably) shorter p arms acrocentric - just stalk of DNA - short arm reduced to vestibule of DNA
53
Robertsonsian translocation occurs
between acrocentric chromosomes can be homologous or non-homologous most common 13and14, 14and15, 14and21
54
Effects of robertsonian translocation
affects 1 in 1000 people most people show no affects can cause problems in offspring

POM 5: Genetics (7 decks)

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