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GIM > cytogentic basis of inheritance > Flashcards

cytogentic basis of inheritance Flashcards

1
Q

define cytogenetics

A

study of chromosomes within a cell.

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2
Q

what is conventional cytogenetic analysis

A

metaphase chromosome analysis (chromosomes are condensed and can be visible)
G banding

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3
Q

what is molecular cytogenetics

A

cytogenetics analysis at the molecular resolution at all stages of the cell cycle- DNA in situ.

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4
Q

examples of molecular cytogenetics

A
  • FISH
  • Microarray CGH
  • Next generation sequencing (NGS)
  • MLPA
  • QF-PCR
  • qPCR
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5
Q

How long does the cell cycle take

A

24hrs

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6
Q

what are the different stages in the cell cycle

A 
growth phase 1
synthesis
growth phase 2
mitosis
cytogenetics
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7
Q

how long is growth phase 1 of the cell cycle and what happens during this phase

A

6-12 hrs

cellular components are duplicated excluding chromosomes.

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8
Q

how long is the synthesis phase of the cell cycle and what happens during this phase

A

6-8 hrs

each of the 46 chromosomes is duplicated by the cells.

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9
Q

how long is growth phase 2 of the cell cycle and what happens during this phase

A

3-4 hrs

the cell double checks the duplicated chromosomes for errors and make needed repairs.

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10
Q

how long is mitosis

A

1 hr.

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11
Q

What are the stages of mitosis

A

Interphase, prophase, metaphase, anaphase, telophase and cyokinetics.

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12
Q

what happens in each stage of mitosis

IMPACT

A
  • Interphase- all chromosomes loose
  • Prophase- chromosome condense
  • Metaphase- chromosome (made of 2 chromatids)- line up along the midline.
  • Anaphase- the sister chromatids are separated
  • Telophase- the cell begins to split into 2
  • Cytokinesis- cell splits in 2 cells and chromosomes unwrap again.
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13
Q

In what stage of the cell cycle does G banding take place

A

metaphase.

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14
Q

How are chromosomes laid out on the template slide for G-banding.

A

line up chromosomes 1- 23, paired up and in order.

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15
Q

what are the main 2 types of cytogenetic abnormalities.

A

numerical

structural

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16
Q

what is the dosage effect

type of cytogenetic abnormality

A

gain or loss in chromosome number

loss is worse

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17
Q

How can a gene be disrupted

A

breakpoint, inappropriate activation/ inactivation.

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18
Q

define genomic imprinting

A

alleles from 1 parent are suspended.

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19
Q

what is the position effect on a gene

A

A gene in a new chromosomal environment functions inappropriately

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20
Q

what has a more severe phenotype sex chromosome imbalance or autosomal imbalance.

A

autosomal imbalance.

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21
Q

define anueploidy

A

gain (trisomy) or loss (monosomy) of chromosomes

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22
Q

define polyploidy

A

gain whole sets (triploidy or tetraploidy)

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23
Q

define mosacism

A

diploidy and anueploidy is one human genome.

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24
Q

where do numerical abnormalities arise ( in which stage of cell development)

A

gametogenesis (meiosis- most errors in female meiosis)
fertilisation
early cleavage (post zygotic non disjunction).

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25
Q

what factors increase the risk of numerical abnormalities in chromosomes during gametogenesis.

A

maternal age >35

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26
Q

what are the stages in meiosis.

A 
prophase 1- DNA replicate
Metaphase 1- chiasmta visible
Anaphase 1- chromosome separation
Telophase- cells begin to separate
Cytokinesis- secondary gametocyte.
Meiosis 2 - sister chromatics are pulled apart.
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27
Q

what is the most common meiotic error

A

non disjunction

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28
Q

when does chromosome disjunction occur in meiosis and what does it form

A

meiosis 1
2 disomic gametes ( which have twice the content of normal gametes)
2 nullisomic gametes ( no content)

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29
Q

when does chromatid disjunction occur in meiosis and what does it form

A

meiosis 2

1 disomic 1 nullisomic and 2 normal gametes.

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30
Q

most common 3 autosomal anueplodiues

A

Trisomy 21, trisomy 18 and trisomy 13.

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31
Q

what are the head abnormalities seen in a patient with trisomy 21

A

Eyes: upward slanting; brushfield spots (on iris)
Nose: Small
Ears: abnormally shaped/low set
Tongue: protruding
General – flat face, brachycephalic, short neck .

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32
Q

what percentage of children with trisomy 21 spontaneously abort

A

75%

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33
Q

what are the neurological abnormalities seen in a patient with trisomy 21.

A

Learning disabilities (mild to moderate IQ 30-60)

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34
Q

what are the hands and feet abnormalities seen in a patient with trisomy 21.

A

single palmar crease
short broad hands
5 th finger clinodactyly- small finger.
wide sandal gap.

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35
Q

what fertility problems do males and females with trisomy 21 face

A

females none.

males infertile.

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36
Q

what other conditions are individuals with trisomy 21 more prevalent to.

A

alzheimer’s
hypothroid
obesity/ coeliac, arthritis, diabetes, hearing loss seizures.

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37
Q

what percentage of trimsomy 18 spontaneously abort

A

95%

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38
Q

what head abnormalities seen in a patient with trisomy 18.

A

microcephaly, low set ears, micrognathia (small jaw), cleft lip and palate

39
Q

what are the hands and feet abnormalities seen in a patient with trisomy 18.

A 
clenched hands (seen on scan)
polydactyly
overlapping fingers (rocker bottom feet).
40
Q

what mental abnormalities seen in a patient with trisomy 18.

A

mental retartdation.

41
Q

what organ malformation occurs in trisomy 18

A

umbilical and inguinal hernia
congenital heart disease
congenital kidney abnormality
eye abnormality (cataracts and micropthalmia)

42
Q

what percentage of trisomy 13 spontaneously abort

A

95%

43
Q

what are mental abnormalities seen in a patient with trisomy 13.

A

Mental retardation severe
Microcephaly/ sloping forehead
Defects of brain – holoprosencephaly

44
Q

What are the hand and feet abnormalities of trisomy 13

A

Polydactyly & fingers flexed

45
Q

what are the head abnormalities of trisomy 13

A

Eyes – microphthalmia, coloboma, retinal dysplasia, palpebral fissures slanted
Cleft lip and/or palate
Ears abnormal and low
Can have Cyclops

46
Q

what other abnormalities of trisomy 13 are evident

A

Heart defect

Abnormal genitalia

47
Q

what types of structures of the human body does trisomy 13 present with

A

midline structures are affected

48
Q

How long do female eggs stay in meiosis 1

A

foetus 5 months until puberty

49
Q

when do eggs go into meiosis 2

A

once they have been fertilised or bleed out in puberty.

50
Q

what is age dependent deterioration of meiotic structures

A

long the eggs stay in meiosis 1 more likely the environment will impact them) - hormonal imbalance, irradiation, oral contraceptives, alcohol

51
Q

Are sex chromosome anueploidies age dependent

A

no

52
Q

Are autosomal anuplodies age dependent

A

Yes- maternal age.

53
Q

give 2 examples of conditions which are sex chromosome anueplodiy

A

Turners (45 X)

Klinefelter. (47XXY)

54
Q

What reproductive problems are faced with turners syndrome

A

Loss of ovarian function
No puberty
Infertility

55
Q

what lymphatic problems do people with turners syndrome face

A

Webbed neck

Swelling of hands &/or feet

56
Q

what other abnormalities do people with turners have

A

Skeletal Abnormalities – short stature
Coarctation of aorta
IQ generally normal/reduced compared to sibs

57
Q

how is klinefelters diagnosed

A

infertility or hypogonadism.

58
Q

what fertility problems do patients with klinfelters face.

A 
lack secondary sexual characteristics
Testicular dysgenesis (abnormal development.
gynaecomastia
59
Q

what growth problems do people with linfelters face

A

Normal in infants, then accelerates

Adults long legs and arms

60
Q

What are the 2 main errors in fertilisation

A
  1. Polyploidy (usually triploidy)

2. Molar pregnancy (double paternal, no maternal)- no genetic content.

61
Q

what percentage of triploides spontaneously abort

A

99.9%

62
Q

define digmy

A

twice the genetic content in egg

63
Q

define diplospermy

A

twice the genetic content in the sperm.

64
Q

define dispermy

A

2 sperm fertilise 1 egg

65
Q

what is the consequence of double maternal content

A

small placenta
Macrocephaly - all available nutrients fo to the brain to ensure survival.
significant grwoth delay.

66
Q

what is the consequence of double paternal content

A

massive placenta

some growth delay

67
Q

what does the maternal genome code for foetus or placenta

A

foetus

68
Q

what does the paternal genome code for foetus or placenta

A

placenta

69
Q

consequences of a molar pregnancy

A

Double paternal genome

Massive cystic placenta

70
Q

define molar pregnancy

A

haploid sperm and empty egg results in haploid zygote

71
Q

when does monocaism happen

A

post zygotically.

72
Q

2 main types of chromosome rearrangements

A

Translocation

Inversion

73
Q

2 types of translocations

A

reciprocal

robertsonian

74
Q

2 types of inversions

A

pericentric

paracentric

75
Q

what is reciprocal translocation

A
  • Break and exchange

* Content is the same just rearranged

76
Q

each type you break a chromosome what is the % chance that you will break a gene

A

3%

77
Q

what is a robertsonian translocation

A

whole arm fusion

78
Q

what chromosome undergo robertsonian translocation

A

acrocentrics-13,14,15,21,22

79
Q

does the long q arm of short p arm contain DNA information

A

long q arm.

80
Q

is there reproductive risk in robertsonin and reciprocal translocation

A

Yes

81
Q

define pericentric inversion

A

breaks either side of centromeres

82
Q

what is paracentric inversion

A

breaks on one side of the chromosome.

83
Q

do inversion have a reproductive risk

A

Yes

84
Q

In robertsonian tranlocations is the phenotype of the patient affected

A

No, all genetic material is still present

q ars fuse and p are lost (but p has no genetic information)

85
Q

unbalanced rearrgaments can be caused by

A

CNV- copy number variation

Deletions and duplications

86
Q

2 types of deletions

A

Interstitial

terminal

87
Q

what is a interstitial deletion

A

segment lost from within the chromosome.

88
Q

what is a terminal deletion

A

segment lost from the end of the chromosome.

89
Q

what is worse a chromosome loss of duplication

A

loss

90
Q

what causes the phenotype in deletions and duplications

A

abnormal gene dosage.

91
Q

what causes deletions and duplications to occur

A
  • Mediated by low copy repeats or duplications.
  • Defined regions of repetitive DNA
  • So when chromosome line up the similar regions can mismatch and pair together.
  • Chaismata occurs leading to deletion and duplication.
92
Q

what causes variable clinical expression of deletions and duplications

A

variable size of imbalance, other genetic and environmental effects

93
Q

what is a ring chromosome

A

terminal ends of a chromosome are detached and then it forms a ring structure (one end attaches to the other)

GIM (14 decks)

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