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PSYCH > Chromosomal Abnormalities > Flashcards

Chromosomal Abnormalities Flashcards

1
Q

What is meant by the karyotype?

A

It is the chromosome set o an individual species in terms of number and structure of chromosomes

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2
Q

How many chromosomes do humans have?

A

22 pairs of normal chromosomes, 1 pair of sex chromsomes

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3
Q

What is a nucleosome?

A

When the DNA is wrapped around the histone proteins

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4
Q

When nucleosomes condense, what is formed?

A

A chromatin fibre

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5
Q

What is formed when chromatin condenses?

A

Chromosome

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6
Q

How do very long DNA molecules fit into the cell?

A

The DNA is wrapped around histones, forming nucleosomes which are then coiled into the chromatin fibre which is then further condensed to fit into the chromosome

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7
Q

Which cells do not contain chromatin?

A

Red blood cells

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8
Q

During what phase of mitosis are chromsomes usually karyotypes and why?

A

During metaphase, as the chromosomes are less condensed

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9
Q

Which cells are commonly chosen to be karyotyped and why?

A

White blood cells as they easily enter into mitosis

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10
Q

What is the short arm of a chromosome called?

A

The p arm

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11
Q

What is the long arm of the chromosome called?

A

The q arm

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12
Q

What connects the p arm with the q arm?

A

A centromere

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13
Q

What is added when karotyping to prevent mitosis from progressing past the metaphase?

A

Colchicine

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14
Q

How are the chromosomes released from the cell?

A

During karyotyping, a hypotonic solution is added, which causes the cell to swell and burst, releasing all the chromosomes

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15
Q

What is used during karyotyping to fix the chromosomes in place on the glass slide?

A

Carnoys fluid

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16
Q

what is carnoys fluid?

A

A combination of acetic acid and ethanol used to fix the chromosomes in place

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17
Q

What are the tips of the chromosome called?

A

Telomere

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18
Q

What staining technique is used in karyotyping?

A

Giemsa staining

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19
Q

What does giemsa staining produce?

A

Banding patterns on the chromosomes

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20
Q

How are the bands on chromosomes numbered?

A

The bands closest to the centromere is 1, and they increase in number the further you get from the centromere

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21
Q

What do dark bands on the chromosomes represent?

A

Heterochromatin - this is where the DNA is wrapped more tightly around the histone proteins and is more condensed

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22
Q

What do light bands on chromosomes represent?

A

Euchromatin - where the DNA is not packed as tightly around the chromatin so it is more open

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23
Q

What is meant by metacentric chromosomes?

A

Where the p arm and the q arm are the same length

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24
Q

What are submetacentric chromosomes?

A

Where the p arm is shorter than the q arm

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25
What is meant by acrocentric chromosomes?
Where the short p arms have been reduced to a stump and replaced by non-coding satellites
26
What type of translocation can acrocentric chromosomes undergo?
Robertsonian translocations
27
What is a robertsonian translocation?
Where there is translocation between two acrocentric chromosomes which results in the formation of one chromosome with normal lengthed arms, and one where the two satellite sections have combined = loss of chromosome
28
Which chromosomes do Robertsonian translocations usually occur in?
13, 14, 15, 21 and 22
29
What is meant by a de novo abnormality?
A chromosomal abnormality which is not inherited from the parents
30
During what stage does cross-over occur?
During prophase of meiosis 1
31
What is the purpose of meiosis?
To reduce the diploid number to haploid so that diploid zygotes can be formed To ensure there is genetic variation amongst off spring
32
What is the purpose of mitosis?
For growth, repair and replace exhausted daughter cells - helps to maintain diploid number
33
Describe how crossing over occurs?
The pairs of homologous chromosomes align, chiasma form and sections of DNA are exchanged
34
What is a recombinant chromatid?
A chromatid in which sections of DNA have been swapped during cross over
35
What is monosomy?
A loss of a chromosome - so now the chromosome only consists of one chromatid
36
What is trisomy?
Where there is a gain of a chromosome, 3 copies of chromosomes
37
What is the most common cause of numerical chromosomal abnormalities?
Non-dysjunction
38
What is non-dysjunction?
Te failure of homologous chromosomes to separate propoerly during cell division
39
What term is used to describe abnormal chromosome numbers?
Aneuploidy
40
What are the three stages in which chromosomal abnormalities can occur?
Mitosis, meiosis 1 or meiosis 2
41
What is Trisomy 21?
Down syndrome
42
What causes trisomy 21?
failure of the 21s chromosome to separate during egg or sperm development
43
What can be used to rapidly detect pre-natal Trisomy?
Quantitative Flourescence PCR
44
What is the cause of 85-90% of trisomy 21?
Maternal dysjunction
45
What increases the risk of maternal dysjunction?
Increasing maternal age
46
Why does maternal non-dysjunction increase with age?
As you get older there is progressive degradation of factors which hold homologous chromatids together, meaning incorrect separation is more likely to occur
47
What is the karyotype of somene with trisomy 21?
47 + 21, or 47, XX+21
48
What causes turners syndrome?
X monosomy
49
What causes Kleinfelder's disease?
XXY - trisomy where you have an extra X chromsome
50
What is the most common form of aneuploidy?
Sex chromosome imbalance
51
How does the body tolerate an imbalance in sex chromsomes?
The excess X chromsomes get inactivated and Y chromosomes do not contain many genes
52
How are excess X chromosomes silenced?
It is packed into a transcriptionally inactive heterochromatin
53
What is a Barr body?
An inactive X chromosome
54
If excess X chromosomes are silenced, why can some XXY and XXX have effects?
Some genes may be located in the PAR regions - genes in this region behave like autosomal genes and therefore are not inactivated like the rest of the X chromosome
55
What are PAR regions?
Pseudoautosomal regions - contain pseudoautosomal genes that behave like autosomal genes and therefore are not silenced when excess X orY chromosomes are
56
What is it which allows crossing over between X and Y chromosomes?
Psuedoautosomal regions
57
What happens when unequal crossing over occurs?
Duplication and deletion
58
What translocation results in the formation of the Philadelphia gene?
t(9;22)(q34;q11)
59
What condition can the fusion of the ABL and BCR gene lead to?
Chronic Myeloid Leukemia
60
What is haploinsufficiency?
A dominant phenotype in diploid organisms that are heterozygous for a loss of function allele
61
What is genomic imprinting?
Changes to the DNA or chromatin that are inherited but do not affect the DNA sequence
62
How is genomic imprinting achieved?
Through DNA methylation
63
Carriers of balanced translocations have increased risk of what?
Creating gametes with unbalanced chromosome translocations, leading to infertility, miscarriages or children with abnormalities
64
What is the severity of the phenotype dependant on?
The gene content of the affected segment
65
Is trisomy or monosomy usually more tolerated?
Trisomy
66
What are some signs and symptoms of patients with Williams syndrome?
Long philtrum - space between nose and lip Short, upturned nose Arched eyebrows Funny, cocktail party personalities
67
Why is Williams syndrome detected using array Comparative Genome Hybridisation?
The deletion is too small to be detected using karyotyping
68
What are the three types of structural chromosomal abnormalities that can occur?
Deletion, duplication and inversion
69
What can be seen when higher levels of karotyping resolution is done?
Sub-bands and sub-sub bands
70
Most aneuploidy caused by non-disjunction arises in what process?
Oogenesis
71
Is paternal age a risk factor for aneuploidy?
No
72
What three conditions are affected by the paternal age effect?
Apert syndrome Crouzon syndrome Pfeiffer syndrome
73
Although paternal age is not a risk factor in aneuploidy, what is?
Smoking
74
How many times per chromosome per cycle of meiosis does cross over occur?
1-3 times
75
What are some signs and symptoms of 7q11.23 duplication syndrome?
``` Delayed speech development Autistic behaviours that affect social interaction and communication Dilatation of the aorta Flat eyebrows Broad nose and short philtrum ```
76
What is meant by mosacism?
The presence of two or more populations of cells with different genotypes eg a person has two sets of DNA so not all cells will have the same genetic material
77
what are the two causes of mosaicism?
Mitotic disjunction during embryonic development Loss of extra chromosome in early development
78
What is paracentric inversion?
Inversion not around the centromere
79
What is pericentric inversion?
Inversion of a section of the chromosome, around the centromere

PSYCH (78 decks)

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