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POM GENETICS > Chromosomal Abnormalities > Flashcards

Chromosomal Abnormalities Flashcards

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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

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
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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26
Q

What type of translocation can acrocentric chromosomes undergo?

A

Robertsonian translocations

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27
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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28
Q

Which chromosomes do Robertsonian translocations usually occur in?

A

13, 14, 15, 21 and 22

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29
Q

What is meant by a de novo abnormality?

A

A chromosomal abnormality which is not inherited from the parents

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30
Q

During what stage does cross-over occur?

A

During prophase of meiosis 1

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31
Q

What is the purpose of meiosis?

A

To reduce the diploid number to haploid so that diploid zygotes can be formed

To ensure there is genetic variation amongst offspring

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32
Q

What is the purpose of mitosis?

A

For growth, repair and replace exhausted daughter cells - helps to maintain diploid number

33
Q

Describe how crossing over occurs?

A

The pairs of homologous chromosomes align, chiasma form and sections of DNA are exchanged

34
Q

What is a recombinant chromatid?

A

A chromatid in which sections of DNA have been swapped during cross over

35
Q

What is monosomy?

A

A loss of a chromosome - so now the chromosome only consists of one chromatid

36
Q

What is trisomy?

A

Where there is a gain of a chromosome, 3 copies of chromosomes

37
Q

What is the most common cause of numerical chromosomal abnormalities?

A

Non-dysjunction

38
Q

What is non-dysjunction?

A

The failure of homologous chromosomes to separate properly during cell division

39
Q

What term is used to describe abnormal chromosome numbers?

A

Aneuploidy

40
Q

What are the three stages in which chromosomal abnormalities can occur?

A

Mitosis, meiosis 1 or meiosis 2

41
Q

What is Trisomy 21?

A

Down syndrome

42
Q

What causes trisomy 21?

A

failure of the 21s chromosome to separate during egg or sperm development

43
Q

What can be used to rapidly detect pre-natal Trisomy?

A

Quantitative Flourescence PCR

44
Q

What is the cause of 85-90% of trisomy 21?

A

Maternal dysjunction

45
Q

What increases the risk of maternal dysjunction?

A

Increasing maternal age

46
Q

Why does maternal non-dysjunction increase with age?

A

As you get older there is progressive degradation of factors which hold homologous chromatids together, meaning incorrect separation is more likely to occur

47
Q

What is the karyotype of someone with trisomy 21?

A

47 + 21, or 47, XX+21

48
Q

What causes turners syndrome?

A

X monosomy

49
Q

What causes Kleinfelder’s disease?

A

XXY - trisomy where you have an extra X chromsome

50
Q

What is the most common form of aneuploidy?

A

Sex chromosome imbalance

51
Q

How does the body tolerate an imbalance in sex chromsomes?

A

The excess X chromsomes get inactivated and Y chromosomes do not contain many genes

52
Q

How are excess X chromosomes silenced?

A

It is packed into a transcriptionally inactive heterochromatin

53
Q

What is a Barr body?

A

An inactive X chromosome

54
Q

If excess X chromosomes are silenced, why can some XXY and XXX have effects?

A

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
Q

What are PAR regions?

A

Pseudoautosomal regions - contain pseudoautosomal genes that behave like autosomal genes and therefore are not silenced when excess X or Y chromosomes are

56
Q

What is it which allows crossing over between X and Y chromosomes?

A

Psuedoautosomal regions

57
Q

What happens when unequal crossing over occurs?

A

Duplication and deletion

58
Q

What translocation results in the formation of the Philadelphia gene?

A

t(9;22)(q34;q11)

59
Q

What condition can the fusion of the ABL and BCR gene lead to?

A

Chronic Myeloid Leukemia

60
Q

What is haploinsufficiency?

A

A dominant phenotype in diploid organisms that are heterozygous for a loss of function allele- one copy of a gene is inactivated or deleted and the remaining functional copy of the gene is not adequate to produce the needed gene product to preserve normal function

61
Q

What is genomic imprinting?

A

Changes to the DNA or chromatin that are inherited but do not affect the DNA sequence

62
Q

How is genomic imprinting achieved?

A

Through DNA methylation

63
Q

Carriers of balanced translocations have increased risk of what?

A

Creating gametes with unbalanced chromosome translocations, leading to infertility, miscarriages or children with abnormalities

64
Q

What is the severity of the phenotype dependant on?

A

The gene content of the affected segment

65
Q

Is trisomy or monosomy usually more tolerated?

A

Trisomy

66
Q

What are some signs and symptoms of patients with Williams syndrome?

A

Long philtrum - space between nose and lip

Short, upturned nose

Arched eyebrows

Funny, cocktail party personalities

Aortic Stenosis (narrowing)

67
Q

Why is Williams syndrome detected using array Comparative Genome Hybridisation?

A

The deletion is too small to be detected using karyotyping

68
Q

What are the three types of structural chromosomal abnormalities that can occur?

A

Deletion, duplication and inversion

69
Q

What can be seen when higher levels of karotyping resolution is done?

A

Sub-bands and sub-sub bands

70
Q

Most aneuploidy caused by non-disjunction arises in what process?

A

Oogenesis

71
Q

Is paternal age a risk factor for aneuploidy?

A

No

72
Q

What three conditions are affected by the paternal age effect?

A

Apert syndrome
Crouzon syndrome
Pfeiffer syndrome

73
Q

Although paternal age is not a risk factor in aneuploidy, what is?

A

Smoking

74
Q

How many times per chromosome per cycle of meiosis does cross over occur?

A

1-3 times

75
Q

What are some signs and symptoms of 7q11.23 duplication syndrome?

A

Delayed speech development
Autistic behaviours that affect social interaction and communication
Dilatation of the aorta
Flat eyebrows
Broad nose and short philtrum

76
Q

What is meant by mosacism?

A

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
Q

what are the two causes of mosaicism?

A

Mitotic disjunction during embryonic development

Loss of extra chromosome in early development

78
Q

What is paracentric inversion?

A

Inversion not around the centromere

79
Q

What is pericentric inversion?

A

Inversion of a section of the chromosome, around the centromere

POM GENETICS (9 decks)

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