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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
what is a karyotype
a normal male chromosome sequence ie 46,XY
26
what is a telomere
tips of the chromosomes, DNA and protein caps ensures replication of tip, tethers to nuclear membrane
27
what are the symbols for a short arm vs a long arm
``` short = p long = q ```
28
what is a centromere
joins sister chromatids together - essenatial for segregation at cell division
29
what is chromatin made up of
DNA and protein
30
what is a heterochromatid
region of highly condensed DNA not coding for anything
31
what are nubbins
top of some chromosomes contain highly repetitive DNA coding for ribosomal DNA
32
what do these mean in terms of chromosomal anomalies trisomy monosomy/deletion triploid
3x copies of a gene 0.5x copies of a gene 3x copy of entire chromosome set (very severe)
33
what are numerical chromosome anomalies due to
usually due to de novo error in meiosis
34
what does aneuploidy vs polyploidy mean
monosomy vs triploidy
35
what are structural anomalies usually caused by
de novo in error or meiosis but can be inherited
36
what are structural anaomalies made up by
translocations = reciprocal / robertsonain | deletions, duplications / inversions
37
different cell lines in another classification of anomaly in chromosomes what is it called
mosaicism which occurs post-zygotically during mitosis
38
30 devisions of sperm cells results in what at the age of 15
spermatogonium
39
what happens to the the spermatogonium in the production of sperm
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
at the age of 25 how many divisions have their been
310
41
how many cell divisions must occur to produce a human egg cell what occurs at meiosis 1 compared to meiosis 2
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
what is non-disjunction
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
when can disjunction occur and what causes it
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
what is mosaicism
After fertilisation of normal egg, embryo undergoes abnormal separation of chromosomes in 1 cell this can causes two or more cell lines
45
what is mosaic down syndrome
one population of normal cells and second population of triatomic cells, monosomic cell line dies
46
what are sex chromosome number anomalies and what are they caused by
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
what are the causes in percentages of early miscarriages
- 40% apparently normal - 60% abnormal - Trisomy 30% - Monosomy 10% - Triploidy 10% - Tetraploidy 5% - Other chromosome anomalies (structural) 5%
48
what is centric fusion - robertsonian
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
what is reciprocal chromosomal structural anomaly
Reciprocal = breakage of two non-homologous chromosomes, exchange of fragments
50
what are acquired cytogenetic abnormalities
genetic change associated with neoplastic or cancer disease process translocation between chromosomes 9 and 22
51
what do acquired cytogenetic abnormalities causes
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
what is neoplasm follicular lymphoma | heteroploidy in cancer
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
what is a syndrome
a collection of features
54
what is down syndrome caused by
it is an abnormality in overall dosage in genes of chromosome 21
55
what is trisomy 21 and what are the features of it | what would you see in a body ultrasound
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
what are the 3 common types of down syndrome
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
``` what do these mean: 47,XX,+21 -69,XXY = -46,XX,dup(2)(p13p22) = -47,XX,+18 = -47,XX,+13 = -45,X = -47,XXY = ```
``` 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
describe and explain Edward's syndrome
Edward’s syndrome = trisomy 18 1/3000 births Multiple malformations particularly in heart/kidneys Clenched hands with overlapping fingers
59
describe and explain patau syndrome
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
describe and explain kleinfelter syndrome
47,XXY 1/1000 males Infertility (atrophic testes do not produce sperm) Poorly developed sexual characteristics (lack of testosterone) Tall
61
describe and explain turners syndrome
``` 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
what occurs during non disjunction
abnormal splitting of cells during meiosis, end up with 3 chromosomes 1 cell and 1 chromosome other cell
63
what are micro deletions and what are they caused by
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
what is Digeorge syndrome
microdeletion = small mouth, prominent nose, congenital heart defects, common is tetralogy of Fallot (4 features together)
65
what is Williams syndrome
bright eyes, stellate irises, wide mouth, upturned nose, long philtrum, flattened nasal bridge, heart defects, microdeletion chromosome 7
66
what is trader-willi syndrome
truncal obesity, unable to stop eating, short stature, great at jigsaw puzzles, causes defects in hypothalamus, structural brain abnormalities
67
what is cat eye syndrome
inverted duplication, trisomic/tetrasomic chromosome 22, eyes look like cat slits, absence of tissue from coloured part of eyes, abnormal obstruction of anus
68
what is FISH
fluorescence in situ hybridization
69
describe the process of FISH
- 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
what is cytogenetic localisation
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
what is chromosome painting
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
what are the types of topographical classification
Size Centromere position (telocentric, acrocentric, metacentric) Chromomere and heterochromatin patterns High resolution band patterns staining Genes highlighted by DNA probes using FISH
73
what is huntington's disease and what is the disease progression and symptoms
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
hat is familial hypercholesterolaemia
cholesterol deposition in patients, tendon/hands xanthoma (spots/lumps), corneal arcus (ring around iris), high risk for CV disease
75
what is cystic fibrosis
require frequent hospital admissions, physiotherapy, medications, scarring of lungs, needs treating with drugs
76
what is duchenne muscular dystrophy
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
how is PCR used in the clinical environment
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
what can PCR be used for to genetically diagnose
sickle cell, thalassaemias, cystic fibrosis, huntington’s, familial cancer, muscular dystrophies, prenatal diagnosis, carrier identification
79
what is stager sequencing used for
to determine the type of mutation including single base changes
80
``` 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 ```
``` 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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