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Genetics Basics Flashcards

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Biology 101 flashcards
1
Q

What are exons and intron?

A

Exons are a region of a gene that encode for an amino acid in a protein

Introns are regions of a gene that does not code for amino acids in a protein

  • most genetic disorders occur due to errors in exons
  • Some occur due to errors in introns
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2
Q

In which compartment of the cell does Protein folding occur?

A

Endoplasmic reticulum

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3
Q

Where does transcription occur?

A

Nucleus

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4
Q

Where does translation occur? what translates mRNA?

A

Occurs in Ribosomes located on the endoplasmic reticulum
Protein folding also occurs in teh endoplasmic reticulum after translation

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5
Q

What is the role of the golgi aparatus

A

Modification of the newly translated protein, usually via glycosylation
Transportation to area of cell that protein is needed in

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6
Q

WHich structure transports individual amino acids to the ribosome for participation in translation

A

tRNA

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7
Q

What is DNA wrapped around for packaging in the cell?

A

Histone octomers

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8
Q

What is DNA wrapped around a histone octomer called?

A

nucleosome

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9
Q

What are chromosomal microarrays (AKA comparative genomic hybridisation CGH) used to detect?

What can it NOT detect?

A

Used to detect sub microscopic chromosomal imbalances (resolution to about 100kb (killa bases))
- Better than what can be achieved with light microscopy (karyotype)

Useful in first line Ix of syndrome presentations in which there is suspicion for multiple genes deleted or alerted manifesting in a syndrome presentation

Cannot specify the location of an imbalance (suplication of deletion)

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10
Q

What can a karyotype detect that a CMA cant?

A

Balanced translocation
Inversion

these do not involve deletion or duplication of material

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11
Q

What can a CMA detect that a karyotype cant?

A

Micro unbalanced translocation
Micro deletion
Microduplication

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12
Q

What are the two examples of next generation sequencing (NGS)?

A

WHole genome sequencing
Exon only sequencing

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13
Q

How are vawrient in DNA reports when NGS performed?

A

Pathgenic variant
- known to be a cause of disease. Corrolates to clinical picture provvided by clinition -> this is the cause
- 99% likely to be the cause

Likely pathogenic
- 90% chance to be the cause

Vartient of uncertain significant
- Not found in the population but also not in pathogenic databases

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14
Q

What is genetic panel testing?

A

This looks at at specific genes in which mutations are known to cause a certain phenotypes
- gene panels are requested based on phenotype (ie pt with cardiomyopathy -> request cardioM panel)

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15
Q

Why is genetic councelling required?

A

Incidental, unsolicited findings are relativly common
- these could have massive implications on the individual and family

  • Ie may go looking for one gene, but incidentally find another one related to bowel cancer -> next to do intensive screening rest of life
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16
Q

What is FISH?

A

FLourecent in situy hybridisation

If looking for fusion gene then can label the individual genes with dif colors. If see separate colour under the micro then genes are seperate. If see new combined colour then they have fused (fusion gene)

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17
Q

How does non invesive prenatal screening work?

A

Blood test
Look for free floating foetal DNA (from break down of maternal WCC or adiopocytes, or from breakdown of foetal trohoblasts in circulation)
- foetal DNA usually smaller than mothers DNA

If see increased genetic material from chromosome 21, then this indicates that the baby has tri21

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18
Q

Mechanism for downs?

A

Chromosomal non dysjunction in meiosis

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19
Q

Aside from complete trisomy 21, in what other ways can pts have downs syndrome?

A

Translocation 5%
- ie Robertsonium t(14:21)
Mosaicism 2-4%

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20
Q

What is Patau syndrome? WHo is at increased risk of getting?

A

Trisomy 13
1:1300 of general pupulation have rob(13q14q)
- asymptomatic but slightly higher risk of baby with Tri13

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21
Q

What is autosomal recessive inheritance? When to consider?

A

this is when mutations in bother versions of the gene (alleles) is required for the disease to manifest
- Homozygote - same mutation in each allele
- compound heterozygote - different mutation in each gene

Gender independent

Consider when affected pts in same generation or when consanguinity present (esp for rare disorders)

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22
Q

Both parents are hetrozygous for autosomal recessive gene. Their ADULT child is unaffected. What is the chance they are a carier too?

A

2/3

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23
Q

Inheritance of CF? What gene?

A

AR
CFTR (F508 gene)

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24
Q

Inheritance of haemoglobinopathies (inc thal)?

A

AR

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25
Q

Inheritance of haemochromatosis? What gene?

A

AR
(HFE gene)

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26
Q

Inheritance of familial mediteranean fever? What gene?

A

AR
(MEFV gene)

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27
Q

Inheritance of Friedreichs ataxia? What gene?

A

AR
FXN gene

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28
Q

Inheritance of Spinal muscular atrophy? What gene?

A

AR
SMN1

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29
Q

Inheritance of Wilsons disease? What gene?

A

AR
ATP7B

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30
Q

Incidence of autosomal recesive condition is 1:10,000, what is the carrier frequency? (hardy weinburg method)

A

q^2 = incidence of condition = 1/10,000
therfore p=sqrt(1/10000)= 0.01

Carrier = 2pq
For rare conditions assume the frequency of the normal allele p is essentially 1
therefore 2pq=210.01=0.02 (2%)

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31
Q

2x carriers of autosomal recensive gene have child
what is chance of affected child?

A

1/4

32
Q

CFTR gene mutation freq 1:25 in population

General population risk of CF child?

Mother has had CF child with another man. Remarries and has child with seperate new man
What is irsk of child having CF?

A

1/251/25/1/4 = 1/2500

1/1 * 1/25 * 1/4 = 1:100

33
Q

Mum is carrier of CF gene
Father has test that is neg for gene but is only 85% sensative
Risk of Baby with CF?

A

fathers risk of carier = 15% of his background risk 1/25
= 0.15 * 1/25

Risk of bb with CF = 1/1 * (0.15*1/25) * 1/4 = 1/666

34
Q

What is autosomal dominant?

A

Mutation in 1 of the 2 alleles is required for the disease
- Chance of having an offspring with disease with 1/2
- therefore if see pedigree with each generation affects regardless of gender think AD

Note the pernetrance of the mutation can be different or can change
- therefore can get from a parent who had the mutation by no phenotytpe

Mutation can also occur de novo

35
Q

Genetic 3x mechanisms behind AD conditions?

A

Haploinsufficiency:
- need 2 working copies of gene. only one of yours is Missing
- most common

Dominant negative
- need 2 working genes. One is mutated so isnt working properly

Gain of function
- mutation of one allele leads to gain in function leading to condition

36
Q

Inheritance of Neuroifibromatosis?

A

AD

37
Q

Inheritance of Tuberous sclerosis complex?

A

AD

38
Q

Inheritance of myotonic dystrophy?

A

AD

39
Q

Inheritance of Huntingtons?

A

AD

40
Q

Inheritance of familial hypercholesterolaemia?

A

AD

41
Q

Inheritance of marfans / ehlers danlos / osteogenesis inperfecta?

A

AD

42
Q

Inheritance of adult PKD?

A

AD

43
Q

Inheritance of BRCA1/2?

A

AD

44
Q

Inheritance of MEN?

A

AD

45
Q

Inheritance of lynch / HNPCC?

A

AD

46
Q

Cause of huntingtons? What gene?
- how many repeats need for very certain will have disease

A

Triplet expansion (CAG)n in the HTT gene
- >40 rpts

47
Q

What is anticipation? example disease?

A

Expansion in transmission with each generation
- Huntingtons disease shows paternal anticipation

48
Q

Pt brother has HD
Pt is 45, nil clinical HD

Age related penetrance of HD is 50% at age 45, rising to 100% by 70yrs

What is risk pt will dev HD later in life (ie what is risk he has the gene)

A

Probability of inherited gene = 1/2
IF inherited gene, probability of normal at 45 = 1/2
- Therefore, risk of having gene = 1/2 * 1/2 = 1/4

Probability of not inherited gene = 1/2
IF not inherited gene, probability of normal at 45 = 1
- Therefore, risk of not having gene = 1/2 * 1 = 1/2

Total risk at age 45 = 1/4 + 1/2 = 3/4
- Conditional prob of having gene = (1/4)/(3/4) = 1/3
- Conditional prob of not having gene = (1/2)/(3/4) = 2/3

Answer 1/3

49
Q

In regards to predictive genetic testing in children (<18) what is the most important consideration?

A

Imacpt on amangemnt
- Only screen if will affect management

50
Q

What is mosaicism?
Is this more associated with AD or AR inheritance?

A

This is when the genetic change occured after fertilisation
- can occur at the gene or chromosome level

More associated with AD
- can occur with AR but would much more unlikely because need two genes affected to manifest

51
Q

What is imprinting?

A

THis is the differential gene expression depending on the parent of origin
- Ie gene may be expressed if inherited from dad, but not expressed if inherited from mum

52
Q

What type of geneitic disorders usually display anticipation?

A

Triplet repeat disorders (think of huntingtons disease)

53
Q

Pt has neurologic disorder that demonstrates anticipation. Which Ix most likely to find the specific genetic mutation responsible?

A

PCR and amplicon length analysis
- this person has anticipation which means that they have a triplet repeat disorder. therefore which test can ID a triplet repeat disorder best
- FISH cant, CMA/CGH cant, karyotypical cant

54
Q

Pt has myotonic dystrophy, has full symptoms.
Father only has mild reduced grip strength.
What is underlying genetic abnormality the explains this?

A

Triplet repeat
- Myotonic dystrophy is triplet repeat disorder
- displays anticipation

55
Q

Which condition is associated with cafe au lait macules?
What is the genetics of this condition?

A

neurofibromatosis
- AD
- If found on one part of teh body may suggest somatic mosaicism

56
Q

What is heteroplasmy? how is it relevant?

A

This is when two or more varients of mtDNA occur in the same cell.

At cell division, mt DNA is distributed randomly and unequally and does not nec reflect ratio found in progenitor cell
This means daughter cell may recieve more of the effected mtDNA than mother had.
This process can continue each generation until threshold is crossed and pt displays condition

57
Q

What is somatic mosaicism? What are clues somatic to mosaicism?

A

This is when there is a mutation on one line of cells early in development leading to a population of cells with a genetic abnormality
- abnormal pigmentation following the lines of Blashko

58
Q

What is germline mosaicism?

A

This is when teh dominant mutation is seen in germ cells and not other somatice cells
- pt often unaffected, can cause full phenotype in offspring

59
Q

Renal angiomyolipomas are associated with which genetic condition?

A

Tuberous sclerosis

60
Q

Can somatic mosaics also have gonadal mosaicism?

A

yes
- but not the otherway around

61
Q

Most common condition due to mosaicism at chromosomal level?

A

Turners syndrome
- 45X (single X chrome missing)
- only affects females

62
Q

Most common conditions due to mosaicism at genetic level?

A

NF1
Tuberous sclerosis

63
Q

Difference between a chimera and mosaicism?

A

Chimera has two or more genetically different cell lines derived from two or more zygotes
- two fertalised eggs produce two cell lines that then fusion or exchange cells to form a population with both in it
- iatrogenic chimeria can be due to transplantation (ie bone marrow transplant)

Mosaic comes from one fertalised egg

Chimera is very rare, most often a distractor

64
Q

Why is trisomy X (47XXX) mostly asymptomatic and yet down syndrome is not?

A

X inactivation

65
Q

Why does X inactivation exist (lyon hypothesis)?

A

this is teh process by which gene equivalent is achieved between females and male?
- X chrome is large lots of gene
- Y chrome is small few genes

66
Q

Can a female ever have an X linked condition? How (2x situiations) ?

A

Yes
In rare situations, there can be skewing of the X inactivation such that the normal X chrome is inactivated. making the female act genetically more like a male
- Most X inactivation occurs with a 50% ratio (ie both are half inactivated) rather than one completle inactivated

Also X linked dominant conditions (much rarer than X linked recessive)

67
Q

Features of X linked on pedigree?

A

No male to male transmission

68
Q

What is the difference between mitochondrial dysfunction and mitochondrial mutation / inheritance?

A

Most mt proteins are coded for in nucleus, not mtDNA. Therefore can have mt dysfunction without mt mutations or inheritance
- therefore most disorders of mt dysfunction with follow autosomal patttern, some with show mt inheritance

69
Q

Where does mtDNA come from? what is the implication for transmission pattern?

A

Mother, therefore offspring of affected male are not affected
- Dif from X linked in that males cant give to daughter or son, whereas in X linked males cant give to son but could give to daughter

70
Q

Difference between mt inheritance and X linked inheritance?

A

mt: nil male transmission
X linked: nil male to male (can have male to female)

71
Q

How is imprinting achieved?

A

Methylation at gametosis
- form of epigenetics

72
Q

Paternal imprinting. is father or mothers gene silenced?

A

imprinting = silenced

therefore:
paternal imprinting = paternal silenced

73
Q

WHat sort of genetic defect will sequencing not readily detect?

A

Large deletions
- too busy looking for the small deletions

May need to do CMA for this

74
Q

Splice site mutation at end of intron. How many amino acids missing in gene?

A

Splice sit mutation at end of intron may result in the foillowing exoin not being read
therefore if next exon has 150 nucleosides, then there will be 50 missing amino acids (3 nucleosides=1 amino acid) because the exon is not read

75
Q

Class of CFTR defects?

A

Class 1 - no CFTR creaated
Class 2 - CFTR created bust doesnt fold right (doesnt reach the surface) - delF508 (most common)
Class 3 - CFTR reachs teh surface but does function properly
CLass 4 - CFTR reaches surface but channel doesnt open
CLass 5 - CFTR is good but not enough produced

Different gene associated with these dif mutations

76
Q

CFTR molecular targets in CF. Give three classes of drugs and example?

A

Correctors - improve CFTR production and processing (ie folding)
- Lumacaftor

Poitentiators - improves opening of the Chloride channel
- Ivacaftor

Chaperone - chaperones the CTFT protein the the surfasce
- Tazacaftor

77
Q
A

Genetics (1 decks)

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