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GENETICS my version > Chromosomal Abnormalities > Flashcards

Chromosomal Abnormalities Flashcards

1
Q

What is meant by the karyotype?

A

It is the chromosome set of 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

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

A

During metaphase, as the chromosomes are less condensed

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4
Q

Which cells are commonly chosen to be karyotyped and why?d

A

White blood cells as they easily enter into mitosis

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5
Q

What is the short arm of a chromosome called?

A

The p arm

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6
Q

What is the long arm of the chromosome called?

A

The q arm

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7
Q

What connects the p arm with the q arm?

A

A centromere

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8
Q

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

A

Colchicine

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9
Q

How are the chromosomes released from the cell? d

A

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

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10
Q

What are the tips of the chromosome called?

A

Telomere

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11
Q

What staining technique is used in karyotyping?

A

Giemsa staining

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12
Q

What does giemsa staining produce?

A

Banding patterns on the chromosomes

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13
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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14
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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15
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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16
Q

what does bph mean in giesma staining?

A

bands per haploid set

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17
Q

what do the bands in giesma staining NOT represent?

A

genes or family of genes - rather, show regions of different compaction

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18
Q

what is aneuploidy?

A

abnormal number of chromosomes

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19
Q

What is meant by metacentric chromosomes?

A

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

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20
Q

What are submetacentric chromosomes?

A

Where the p arm is shorter than the q arm

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21
Q

What is meant by acrocentric chromosomes?

A

Where the short p arms have been reduced to a stump and replaced by non-coding satellites

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22
Q

What type of translocation can acrocentric chromosomes undergo?

A

Robertsonian translocations

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23
Q

What is a robertsonian translocation?

A

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

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24
Q

Which chromosomes do Robertsonian translocations usually occur in?

A

13+14; 14+15; 14+ 21

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25
What is meant by a de novo abnormality?
A chromosomal abnormality which is not inherited from the parents but occur in individual gametes during spermatogenesis and oogenesis
26
During what stage does cross-over occur?
During prophase of meiosis 1
27
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 enables random assortment of homologues and recombination
28
What is the purpose of mitosis?
For growth, repair and replace exhausted daughter cells - helps to maintain diploid number
29
Describe how crossing over occurs?
The pairs of homologous chromosomes align, chiasma form and sections of DNA are exchanged
30
What is a recombinant chromatid?
A chromatid in which sections of DNA have been swapped during cross over
31
What is monosomy?
A loss of a chromosome - so now the chromosome only consists of one chromatid
32
What is trisomy?
Where there is a gain of a chromosome, 3 copies of chromosomes
33
What is the most common cause of numerical chromosomal abnormalities?
Non-dysjunction
34
What is non-dysjunction?
Te failure of homologous chromosomes to separate propoerly during cell division
35
What term is used to describe abnormal chromosome numbers?
Aneuploidy
36
What are the three stages in which chromosomal abnormalities can occur?
Mitosis, meiosis 1 or meiosis 2
37
What is Trisomy 21?
Down syndrome
38
What causes trisomy 21?
failure of the 21s chromosome to separate during egg or sperm development
39
What can be used to rapidly detect pre-natal Trisomy? d
Quantitative Flourescence PCR
40
What is the cause of 85-90% of trisomy 21?
Maternal dysjunction
41
What increases the risk of maternal dysjunction?
Increasing maternal age
42
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
43
What is the karyotype of somene with trisomy 21?
47 + 21, or 47, XX+21
44
What causes turners syndrome?d
X monosomy
45
What causes Kleinfelder's disease? d
XXY - trisomy where you have an extra X chromsome
46
What is the most common form of aneuploidy?
Sex chromosome aneuploidy
47
Why does the body tolerate an imbalance in sex chromsomes but other autosomal ones are not?
in females, one of the excess X chromsomes get inactivated and Y chromosomes do not contain many genes, so in general, fewer genes are affected
48
in sex chromosomes, why if inactivated does abnormal X have effects?
both X + Y chromosomes have PAR PAR = pseudo-autosomal regions
49
what are PAR regions
pseudo-autosomal regions which still produces genes and doesn't get inactivated
50
What is a Barr body? d
An inactive X chromosome
51
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
52
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
53
What is it which allows crossing over between X and Y chromosomes?
Psuedoautosomal regions
54
What happens when unequal crossing over occurs?
Duplication and deletion
55
What translocation results in the formation of the Philadelphia gene?
t(9;22)(q34;q11)
56
What condition can the fusion of the ABL and BCR gene lead to?
Chronic Myeloid Leukemia
57
What is haploinsufficiency? d
A dominant phenotype in diploid organisms that are heterozygous for a loss of function allele
58
What is genomic imprinting? d
Changes to the DNA or chromatin that are inherited but do not affect the DNA sequence
59
How is genomic imprinting achieved?
Through DNA methylation
60
Carriers of balanced translocations have increased risk of what?
Creating gametes with unbalanced chromosome translocations, leading to infertility, miscarriages or children with abnormalities
61
What is the severity of the phenotype dependant on?
The gene content of the affected segment
62
Is trisomy or monosomy usually more tolerated?
Trisomy
63
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
64
Why is Williams syndrome detected using array Comparative Genome Hybridisation?
The deletion is too small to be detected using karyotyping
65
What are the three types of structural chromosomal abnormalities that can occur?
Deletion, duplication and inversion
66
What can be seen when higher levels of karotyping resolution is done?
Sub-bands and sub-sub bands
67
Most aneuploidy caused by non-disjunction arises in what process?
Oogenesis
68
Is paternal age a risk factor for aneuploidy?
No
69
What three conditions are affected by the paternal age effect?
Apert syndrome Crouzon syndrome Pfeiffer syndrome
70
Although paternal age is not a risk factor in aneuploidy, what is?
Smoking
71
How many times per chromosome per cycle of meiosis does cross over occur?
1-3 times
72
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
73
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
74
what are the two causes of mosaicism?
Mitotic disjunction during embryonic development Loss of extra chromosome in early development

GENETICS my version (9 decks)

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