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IMS > Clinical genetics > Flashcards

Clinical genetics Flashcards

1
Q 
define these terms:
polygenic 
genotype 
phenotype 
monogenic 
multifactoral 
chromosome disorders
A

influence of many genes
variants/changes/mutations in a gene
single gene disorders
variants in genes causing alterations in function and from the environment
chromosomal imbalance causes lateration in gene dosage, huge groups of genes changes and imbalance of proteins produced

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2
Q

what are the different types of genetic mutation classifications

A

multifactoral, single gene, chromosomal, mitochondrial, somatic mutations (cancer)

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3
Q

what is:
penetrance
mendelian
multifactoral

A

way genotype expresses itself as a phenotype
always definitely caused by genotype
other factors involved

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4
Q

what classification of disease is MS

A

multifactorial as genetic factor cause susepctability but individual factor has low penetrance

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5
Q

what are the sub types of single gene disorders

A

dominant
recessive
x linked

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6
Q

define
dominant
recessive
x linked

A

heterozygotes with one copy of altered gene affected
homozygous with two copies of altered gene affected
males with one copy of altered gene on x chromosome affected, females also inherit, difficult to know whether x linked recessive dominant or recessive

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7
Q

what does autosomal dominant mean

what are some example diseases

A

parents diploid, two copies of chromosome, haploid in germ cells, risk of affected off spring is half
dominant PKD, huntingtons, neurofibromatosis

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8
Q

what does autosomal recessive mean and give some example diseases

A 
risk of affected offspring is a 1/4 
risk of carrier in off spring is 1/2
cystic fibrosis 
phenylketouria 
spinal muscular atrophy 
congenital adrenal hyperplasia
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9
Q

what does x linked means in terms of risk of affliction

A 
risk of affected son = 1/2, 
risk of carrier daughter = 1/2
fragile x
haemophillia 
duchenne muscular dystrophy
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10
Q

what does chromosomal imbalance cause

A

alteration of gene dosage

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11
Q

what are the two factors of human disease

A

environmental - common, multifactorial, low recurrence rate

genetic - rare, unifactorial, high recurrence rate

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12
Q

what are the % of causes to cancer

A

sporadic - 75-85%
familial 10-20%
hereditary 5-10%

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13
Q

what does sporadic mean in terms of cancer

A

both alleles of gene become inactivated in a particular somatic cell leading to loss of control of growth and unchecked cell proliferation

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14
Q

what does familial mean in terms of cancer

A

dominantly inherited, altered allele inherited and in all body cells when second normal alley of gene pair becomes inactive in somatic cell leads to loss of cell growth and unchecked proliferation

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15
Q

describe the maternal inheritance of mitochondrial genes

A

all mitochondria occur in ovum - all from mother

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16
Q

give an example of mitochondrial gene disorder and what tissues are most likely to be affected

A

tissues most affected are those that require lots of mitochondria
lever hereditary optic neuropathy = reduced vision, hyperaemia of disc with blurred margains - disc pale colour

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17
Q

what is mitosis compared to meiosis

A

cell division to ensure growth of organism

two successive divisions producing 4 daughter cells

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18
Q 
describe what happens in these phases 
prophase 
metaphase 
anaphase 
telophase 
interphase
A

chromatin condenses
nucelar envelope disappears, chromosomes align at equatorial plate
sister chromatids separate and centromeres divide
chromatin expands and cytoplasm divides
cellular components are duplicated G1, chromosome duplicated S, cell checks for errors G2

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19
Q

what are the uses of meiosis

A

used only for the production of sperm cells and eggs, reduction division to 23 chromosomes per gamete

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20
Q

why is meiosis necessary for gametes

A

ensures genetically different offspring by crossing over and independent segregation

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21
Q

what are the products of meiosis 1 vs meiosis 2

A

two diploid cells

4 haploid cells

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22
Q

how does gene re-assortment occur via crossing over and when does it occur

A

during meiosis 1 each chromosome duplicates producing 2 sister chromatids
crossing over/recombination - swapping of parts of chromosomes so different genes on different chromosomes
meiosis 2 then occurs

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23
Q 
define these terms on chromosomes 
locus:
allele:
light bands: 
dark bands:
A

position of a gene or genetic marker on the chromosome
alternative forms of gene/marker
DNA less packed and take sup less dye - replication early in S phase, GC rich
DNA tightly packed and takes up more dye - replicate late - AT rich

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24
Q

what are the number and types of chromosomes in the human body

A

46 chromsomes
23 pairs
22 pairs chromsomes
1 pair of sex chromosomes

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25
Q

what is a karyotype

A

a normal male chromosome sequence ie 46,XY

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26
Q

what is a telomere

A

tips of the chromosomes, DNA and protein caps ensures replication of tip, tethers to nuclear membrane

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27
Q

what are the symbols for a short arm vs a long arm

A 
short = p 
long = q
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28
Q

what is a centromere

A

joins sister chromatids together - essenatial for segregation at cell division

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29
Q

what is chromatin made up of

A

DNA and protein

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30
Q

what is a heterochromatid

A

region of highly condensed DNA not coding for anything

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31
Q

what are nubbins

A

top of some chromosomes contain highly repetitive DNA coding for ribosomal DNA

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32
Q

what do these mean in terms of chromosomal anomalies
trisomy
monosomy/deletion
triploid

A

3x copies of a gene
0.5x copies of a gene
3x copy of entire chromosome set (very severe)

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33
Q

what are numerical chromosome anomalies due to

A

usually due to de novo error in meiosis

34
Q

what does aneuploidy vs polyploidy mean

A

monosomy vs triploidy

35
Q

what are structural anomalies usually caused by

A

de novo in error or meiosis but can be inherited

36
Q

what are structural anaomalies made up by

A

translocations = reciprocal / robertsonain

deletions, duplications / inversions

37
Q

different cell lines in another classification of anomaly in chromosomes what is it called

A

mosaicism which occurs post-zygotically during mitosis

38
Q

30 devisions of sperm cells results in what at the age of 15

A

spermatogonium

39
Q

what happens to the the spermatogonium in the production of sperm

A

it divides to form 2 cells - one stays as the same type of sperm but one then continues to divide into 4 separate cells types

40
Q

at the age of 25 how many divisions have their been

A

310

41
Q

how many cell divisions must occur to produce a human egg cell
what occurs at meiosis 1 compared to meiosis 2

A

22 mitotic divisions by 5 months gestation produce 2,600,000 oocytes
Each month one is ovulated
At meiosis 1 1st polar body formed and completed at ovulation
At meiosis 2 2nd polar body formed and completed at fertilisation, producing zygote

42
Q

what is non-disjunction

A

the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.

43
Q

when can disjunction occur and what causes it

A

Incorrect formation of metaphase plate can cause all chromosomes to go to 1 spindle, can result in trisomy 21 (non-disjunction)
Non-disjunction can also occur at meiosis 2, results in 2 normal gametes, 1 with no genetic info and 1 with double genetic info

44
Q

what is mosaicism

A

After fertilisation of normal egg, embryo undergoes abnormal separation of chromosomes in 1 cell
this can causes two or more cell lines

45
Q

what is mosaic down syndrome

A

one population of normal cells and second population of triatomic cells, monosomic cell line dies

46
Q

what are sex chromosome number anomalies and what are they caused by

A

causes problems relating to sexual development and fertility
often presents at puberty or later - sometimes during investigations of infertility
caused by abrnomal gametes with unusual complements of sex chromosomes

47
Q

what are the causes in percentages of early miscarriages

A
  • 40% apparently normal
  • 60% abnormal
  • Trisomy 30%
  • Monosomy 10%
  • Triploidy 10%
  • Tetraploidy 5%
  • Other chromosome anomalies (structural) 5%
48
Q

what is centric fusion - robertsonian

A

chromosomal structural anaomaly
breakage of two acrocentric (centromere near top) chromosomes (13/14/15/21/22), at or close to centromeres, subsequent fusion of long arms, short arms lost

49
Q

what is reciprocal chromosomal structural anomaly

A

Reciprocal = breakage of two non-homologous chromosomes, exchange of fragments

50
Q

what are acquired cytogenetic abnormalities

A

genetic change associated with neoplastic or cancer disease process
translocation between chromosomes 9 and 22

51
Q

what do acquired cytogenetic abnormalities causes

A

Occurs 90% patients with chronic myelogenous leukaemia, leads to continutive expression of fusion gene which encodes tyrosine kinase receptor protein, abnormal signalling blocked by Imatinib

52
Q

what is neoplasm follicular lymphoma

heteroploidy in cancer

A

oncogene translocated from usual site chromosome 18 to new site chromosome 14
Cluster of antibody heavy chain genes expressed in B-lymphocytes
No regulates newly located gene so continually expressed, now protein suppresses cell death by apoptosis
Now cells keep growing and form neoplastic proliferation of B-lymphocytes

53
Q

what is a syndrome

A

a collection of features

54
Q

what is down syndrome caused by

A

it is an abnormality in overall dosage in genes of chromosome 21

55
Q

what is trisomy 21 and what are the features of it

what would you see in a body ultrasound

A

Trisomy 21, 47,XX,+21
Features: round face, protruding tongue, upslanting palpebral fissures (around eye), epicanthic folds, developmental delay
Ultrasound: short femurs, nuchal translucency, echogenic bowel (bright), choreoid plexus (brain) cyst, sandal gap (between 1st and 2nd toe), single palmar crease (due to reduced activity in womb)

56
Q

what are the 3 common types of down syndrome

A

95% have three separate copies of chromosome 21
4% have extra copy due to Robertsonian translocation (stuck on top of another chromosome)
1% have mosaicism with normal and trisomy 21 cell lines (milder features), occurs post-zygotically via non-disjunction (abnormal separation of chromosomes during meiosis)

57
Q 
what do these mean: 
47,XX,+21 
-69,XXY = 
-46,XX,dup(2)(p13p22) = 
-47,XX,+18 = 
-47,XX,+13 =
-45,X = 
-47,XXY =
A 
female down syndrome 
male triploidy 
female 23 chromosomes duplication of short arm of chromosome 2 from bands 13-22
female edwards syndrome 
female pat syndrome 
turner syndrome 
klinefelter syndrome
58
Q

describe and explain Edward’s syndrome

A

Edward’s syndrome = trisomy 18
1/3000 births
Multiple malformations particularly in heart/kidneys
Clenched hands with overlapping fingers

59
Q

describe and explain patau syndrome

A

Patau syndrome = trisomy 13
1/5000 births
Multiple malformations, also causes polydactyly and inguinal hernias
Affects midline structures particularly incomplete lobation of brain, cleft lip, congenital heart disease

60
Q

describe and explain kleinfelter syndrome

A

47,XXY
1/1000 males
Infertility (atrophic testes do not produce sperm)
Poorly developed sexual characteristics (lack of testosterone)
Tall

61
Q

describe and explain turners syndrome

A 
45,X (monosomy X)
1/5000 females
99% lost spontaneously in pregnancy
Short stature
Primary amenorrhoea (ovaries involute before birth)
Congenital heart disease 20%
Puffy feet
Redundant skin at back of neck
62
Q

what occurs during non disjunction

A

abnormal splitting of cells during meiosis, end up with 3 chromosomes 1 cell and 1 chromosome other cell

63
Q

what are micro deletions and what are they caused by

A

bits of chromosome missing too small to be seen down microscope
Spans several genes but very small amount of chromosome
Caused by crossing over during meiosis and confusion during recombination, parts of chromosome deleted once meiosis resolved

64
Q

what is Digeorge syndrome

A

microdeletion = small mouth, prominent nose, congenital heart defects, common is tetralogy of Fallot (4 features together)

65
Q

what is Williams syndrome

A

bright eyes, stellate irises, wide mouth, upturned nose, long philtrum, flattened nasal bridge, heart defects, microdeletion chromosome 7

66
Q

what is trader-willi syndrome

A

truncal obesity, unable to stop eating, short stature, great at jigsaw puzzles, causes defects in hypothalamus, structural brain abnormalities

67
Q

what is cat eye syndrome

A

inverted duplication, trisomic/tetrasomic chromosome 22, eyes look like cat slits, absence of tissue from coloured part of eyes, abnormal obstruction of anus

68
Q

what is FISH

A

fluorescence in situ hybridization

69
Q

describe the process of FISH

A
  • Make a probe complementary to known sequence labelled with fluorescent marker
    Denature known chromosome sequence, can be on dividing or non-dividing cells
    Denature probe, allow to hybridize to complementary sequence
    Wash off excess probe and observe chromosomes under fluorescent microsome
    If microdeletion present won’t be DNA present during DNA denaturing so specific tagged probe won’t be able to recognise complementary DNA and bind
70
Q

what is cytogenetic localisation

A

produces fluorescent signal at site of specific DNA sequence, several probes, each corresponding to defined genomic segment, can be simultaneously analysed and ordered with respect to each other using multicoloured FISH

71
Q

what is chromosome painting

A

spectral karyotyping and multicolour FISH, paint each chromosome 1/24 colours, sky and multicolour differ only in method used to measure spectral characteristics of each pixel in image

72
Q

what are the types of topographical classification

A

Size
Centromere position (telocentric, acrocentric, metacentric)
Chromomere and heterochromatin patterns
High resolution band patterns staining
Genes highlighted by DNA probes using FISH

73
Q

what is huntington’s disease and what is the disease progression and symptoms

A

causes involuntary movements, jerks/ticks, loss of tissue in brain, fatal/no treatment
Usually appears in 30s/40s
Early symptoms = depression, irritability, small involuntary movements, poor coordination, trouble learning new info or making decision
Progressive disease, movements become more pronounced
May have problems walking/speaking/swallowing
Passed generation to generation
Size of repeat in genetic code often increases in size, larger number of repeats = earlier onset, called anticipation

74
Q

hat is familial hypercholesterolaemia

A

cholesterol deposition in patients, tendon/hands xanthoma (spots/lumps), corneal arcus (ring around iris), high risk for CV disease

75
Q

what is cystic fibrosis

A

require frequent hospital admissions, physiotherapy, medications, scarring of lungs, needs treating with drugs

76
Q

what is duchenne muscular dystrophy

A

difficult to stand up, have to brace with arms, weak proximal muscles, disorganisation of muscles, invasion by fibrous tissue and absence of dystrophin on outer membranes

77
Q

how is PCR used in the clinical environment

A

Clinical: genotyping genetic markers, microsatellites, applications in genetic linkage analysis for inherited diseases, tissue typing, detection of mutations, genetic disease diagnosis, cancer diagnosis, identification of candidate disease genes in research setting

78
Q

what can PCR be used for to genetically diagnose

A

sickle cell, thalassaemias, cystic fibrosis, huntington’s, familial cancer, muscular dystrophies, prenatal diagnosis, carrier identification

79
Q

what is stager sequencing used for

A

to determine the type of mutation including single base changes

80
Q 
what do these symbols mean on a lineage tree 
square 
circle 
triangle 
double line 
filled in shape 
shape with line through 
diamond 
"A" shape connecting siblings 
diagonal connecting two siblings 
SB
triangle with line through
A 
male 
female 
spontaneous abortion 
union of consanguineous couple 
affected 
someone who has died 
sex is unknown ie foetus
identical twins 
non-identical twins 
still born 
therapeutic abortion

IMS (20 decks)

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