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Genetics Flashcards

1
Q

What is a triploid mutation?

A

Mutation where threes 69 chromosome

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2
Q

What is a trisomy?

A

Mutation where there is an extra chromosome

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3
Q

Describe autosomal dominant

A

This is where one affected gene is enough to give the disease. There is a vertical pattern of inheritance.

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4
Q

What pattern of inheritance foes autosomal dominant have?

A

Vertical

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5
Q

What differs between autosomal dominant and s-linked conditions?

A

Autosomal dominants conditions can be mistaken for X-linked conditions. If a male passes a mutated gene to a male, then it is confirmed autosomal dominant. This is because the male is passing on the Y chromosome to the male and X to the female.
If a male passes to another male, it is not X-linked.

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6
Q

What is genetic variation?

A

Variable expressivity occurs when a phenotype is expressed to a different degree among individuals with the same genotype.

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7
Q

What is pentrance?

A

This refers to the likelihood that a clinical condition will occur when a particular genotype is present

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8
Q

What is incomplete pentrance?

A

Incomplete penetrance is where someone inherits the mutation but does not have the disorder.

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9
Q

What is complete penetrance?

A

Complete penetrance is where someone who has the inheritance also has the disorder. An example of a complete penetrance is Huntington’s.

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10
Q

What is an example of a condition with complete penetrance?

A

Huntington’s

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11
Q

What are modifier genes?

A

Modifier genetic variants are also common in autosomal dominant conditions. These are genes which can alter the expression or function of another gene or its product. Modifier genes may affect the severity or penetrance. For example, FGFR2 variants in BRCA2 mutation carrier.

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12
Q

Describe autosomal recessive conditions

A

Autosomal recessive conditions involve both parents being carriers and passing on both affected genes. Children who are carriers are known as heterozygous and children with have no inheritance mutation are known as homozygous.

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13
Q

What are carriers of an autosomal recessive condition called?

A

Heterozygous

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14
Q

What is compound heterozygous?

A

This is where there is two different mutated alleles at a a particular gene

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15
Q

What is double heterozygous heterozygous?

A

This is where the is the presence of two different muted allies at two separate genetic locations

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16
Q

Congenital adrenal hyperplasia, is this recessive or dominant?

A

Recessive

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17
Q

What is the pattern in autosomal recessive conditions?

A

Horizontal

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18
Q

In autosomal dominant, is the disease affected in heterozygotes or homozygotes?

A

Heterozygotes

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19
Q

In autosomal recessive, is the disease affected in heterozygotes or homozygotes?

A

Homozygotes

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20
Q

What is an x-linked condition?

A

This is where there is a mutation on the X chromones. There is both recessive and dominant.

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21
Q

Can a male pass an affected X chromosome to their son?

A

No. They pass a Y chromosome to their son. Hence they can pass a x-linked condition to their daughter.

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22
Q

What is an obligate carier?

A

An obligate carrier is an individual who may be clinically unaffected but who must carry a gene mutation based on analysis of the family history.

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23
Q

What is knights move inheritance?

A

Males linked through unaffected females and only males affected

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24
Q

What is skewed X inactivation?

A

This is where inactivation of one X chromone is favoured over the other, leading to an uneven number of cells with each chromosome inactivated. In the early embryo, the X chromosome undergoes x-activation, meaning one x-chromone is turned off. In some cause, the activation may favour the mutated form.

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25
Q

What are some examples x-linked dominant conditions?

A
  • Rett syndrome
  • Vitamine D resistant rickets
  • incontinentia pigmenti
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26
Q

What is genetic anticipation?

A

Genetic anticipation: this is where there is increasing severity and earlier age of onset in successive generations. For example:

  • Huntington’s: a condition of triple repeats with increases with offspirng
  • Fragile x syndrome
  • Myotonic dystrophy
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27
Q

What is the female to male ratio in x-linked conditions?

A

Males are largely more affected

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28
Q

What are some exampes of conditions with genetic anticipation?

A
  • Huntington’s
  • fragile x syndrome
  • myotonic dystrophy
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29
Q

What is pseudo-dominant inheritance?

A

Pseudo-dominant inheritance: this is where inheritance of a recessive trait mimics a dominant pattern. The pattern of inheritance in which a single recessive allele is inherited but is still expressed is known as pseudodominance. This is because of the carrier frequency rate.
An example is Gilbert’s syndrome:
- The carrier frequency is 50%

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30
Q

What is an example of a pseudo-dominant inheritance condition?

A

Gilberts syndrome

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31
Q

Describe mitochondrial DNA

A
  • smaller genome
  • circular
  • 16.6kb
  • 37 genes
  • no introns
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32
Q

Does mitochondria have introns?

A

No

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33
Q

Where is a child’s mitochondria inherited from?

A

The mother.
. If there is a mutated form all children will receive it but with variable extents. The syndrome will affect muscles, brain and eyes.

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34
Q

Give an example of a mitochondria inherited condition

A

Leigh’s disease

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35
Q

Describe Heteroplasmy

A

Mitochondria can affect different siblings in different ways. This is because a mitochondria will contain several DNAs and there is a vast number of different mitochondria. This mixture is known as heteroplasmy (the presence of more than one type of organellar genome).
Heteroplasmy is a feature of mitochondrial heritance.

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36
Q

What is the average onset of Huntington’s?

A

30-50

really long sequence ay occur earlier

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37
Q

What are the main symptoms of Huntington’s?

A
  • progressive chorea
  • dementia
  • psychiatric symptoms

Patients usually underweight due to difficulty eating.

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38
Q

Is Huntington’s dominant of recessive?

A

Dominant

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39
Q

What is the pathological repeat in Huntington’s?

A

In normal people, the Huntington gene located on chromone 4, has a triplet repeat, where the sequence CAG is repeated 10-35 times.
In Huntington’s disease, this repeat goes on for 36 or more times.

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40
Q

What does CAG encode?

A

CAG codes for Glutamine. Therefore, there are extra glutamine and Huntington’s can also be referred to as Polyglutamine. The extra glutamine (polyglutamine tract) aggregates causing neurotoxicity.

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41
Q

Does Huntington’s have genetic anticipation?

A

Yes

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42
Q

When are repeats in the CAG prone to expansion?

A

During meiosis (especially from the father)

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43
Q

Is myotonic dystrophy dominant or recessive?

A

Dominant

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44
Q

Does myotonic dystrophy have genetic anticipation?

A

Yes

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45
Q

What is myotonia?

A

Prolonged muscle contraction

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46
Q

What are some symptoms of myotonic dystrophy?

A
  • Progressive muscle weakness in early adulthood
  • Myotonia: prolonged contraction of a muscle
  • Cataracts
  • there is increased susceptibly for diabetes.
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47
Q

What is the pathological mechanism of myotonic dystrophy?

A

There is an unstable length mutation of CTG in the 3’ (downstream end of the gene) transcribed but not translated region of the DMPK gene.

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48
Q

What gene is affected in myotonic dystrophy?

A

DMPK

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49
Q

The mutation in myotonic dystrophy is not in the coding sequence. How does this cause disease?

A

The reason the mutation causes disease, even though it is not in the coding sequence, is due to an indirect toxic effect upon splicing of other genes e.g. the chloride ion channel CLCN1 gene (causing myotonia) and the insulin receptor gene (susceptibility to diabetes).

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50
Q

What effect does the mutation in myotonic dystrophy have on the CLCN1 gene?

A

The mutation affects the splicing of this gene and this causes myotonia.

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51
Q

Is cystic fibrosis recessive or dominant?

A

Recessive

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52
Q

What is the carrier frequency fo cystic fibrosis?

A

The carrier frequency of 1 in 20 – 1 in 25.

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53
Q

Describe the testing for Cystic fibrosis?

A

The initial test is testing for IFT level (immunoreactivity trypsin) which becomes abnormal if the child is affected. If the child is detected to have the condition, then it can be confirmed with DNA testing.

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54
Q

What are the main symptoms of cystic fibrosis?

A

There are recurrent lung infections and exocrine pancreatic insufficiency (85-90%). Male infertility is also very common.

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55
Q

How many different mutations are in the CFTR gene?

A

100

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56
Q

Describe the most common type of mutation in the CFTR gene?

A

F508del.
This is an in-frame deletion of the third base pain (one codon called phenylalanine) at position 508. This prevents normal folding of the protein and insertion into the plasma membrane.

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57
Q

What is cascade screening?

A

Cascade screening is mechanism for identifying people at risk for a genetic condition by a process of systematic family tracing. Identification of mutations permits prenatal diagnosis if desired and the subsequent identification of carrier relatives.

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58
Q

Is Neurofibromatosis type one (NF1) dominant or recessive?

A

Dominant

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59
Q

What are some symptoms of Neurofibromatosis type one (NF1)?

A
  • cafe au alit macules
  • neurofibromas
  • short stature
  • macrocephaly
  • Lisch nodules on the iris
    It is a condition that can cause tumours to grow.
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60
Q

There is variability expression in Neurofibromatosis type one (NF1). What are some reason for this?

A

There is a variable expressivity. Some reasons for this include:

  • Other genes can have affect (modifier genes)
  • Environmental factors (i.e. somoni being exposed to a lot of radiation)
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61
Q

What are some possible complications of Neurofibromatosis type one (NF1)?

A
  • hypertension
  • scoliosis
  • pathological tubular fractures
  • significant tumours: pheochromocytoma (sudden shoot up in blood pressure), sarcomas and optic pathway gliomas
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62
Q

What condition is pheochromocytoma associated with and what is the common first symptom?

A

Neurofibromatosis type one (NF1)

- sudden increase in blood pressure

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63
Q

Is Duchenne muscular dystrophy recessive or dominant?

A

X-linked rescessive

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64
Q

Is Becker muscular dystrophy recessive or dominant?

A

X-linked rescessive

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65
Q

What is significant about the DMD gene?

A

This is the largest known human gene. It covers 2.4 million base pairs. It provides instructions for making dystrophin.

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66
Q

What is the function of Dystrophin?

A

Dystrophin forms a link between F-actin intracellularly and the dystroglycan complex. If it is not working, there is a disconnection between the outside and inside of a cell.

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67
Q

What is the relationship between SCK and DMD?

A

CK leaks out of damaged muscle fibres into the serum (into blood). Boys with DMD will have massively increased levels of SCK from birth (i.e. before any other symptoms are noticeable).

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68
Q

What is an in-frame mutation?

A

This would not affect the reading frame as the mutation is a multiple of three.

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69
Q

What is an out-of-frame mutation?

A

This is where the mutation is not a multiple of three and this affects the reading frame.

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70
Q

What mutations are more common in Duchenne muscular dystrophy?

A

65% deletions, mostly out of frame

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71
Q

What mutations are more common in Becker muscular dystrophy?

A

85% deletions, most in frame

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72
Q

What is the onset of Duchenne muscular dystrophy?

A

3 years

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73
Q

What is the onset of Becker muscular dystrophy?

A

11 years

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74
Q

What is genotype-phenotype correlation?

A

This is a statistical relationship that predicts a physical trait in a person or abnormality in a patient with a given mutation.

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75
Q

Why is Duchenne muscular dystrophy more serious?

A

The mutation are out of frame meaning the protein is not formed.

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76
Q

Why is muscular dystrophy are commonly affecting boys?

A

This is because the dystrophin gene is on the X chromosome and if the boys inherit a faulty copy, they do not have any others.

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77
Q

Is fragile-x syndrome recessive or dominant?

A

X-linked dominant

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78
Q

Is there genetic anticipation in fragile-x syndrome?

A

Yes

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79
Q

What is the mutation in fragile-x syndrome?

A

Repeats in the 5’ UTR region of FMR1 gene). 5’ is the upstream.

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80
Q

How many repeats make a full mutation in fragile x syndrome?

A

200

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81
Q

What are the two possible mutations for down syndrome?

A

95% of mutations in down syndrome is due to a non-disjunction mutation, where there is failure of chromosome separation.

In some cases, there may be a translocation mutation, where part of the 21 chromosome is placed on another chromosome, for example 14. This is called 14:21 translocation and this is commonly an inherited condition. This is where the long arm of an additional chromosome 21 is placed on chromosome 14.

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82
Q

What are some clinical features of down’s syndrome?

A
  • Small chin
  • Slanted eyes
  • Poor muscle tone
  • Flat nasal bridge
  • Single crease on palm
  • Short neck
  • Excessive joint flexibility
  • Extra space between big toe and second toe
  • Short fingers
  • Small ears
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83
Q

What are some tests for down syndrome?

A

Testing for down syndrome:

  • First trimester test (blood test and ultrasound): PAPP-A decrease, hCG increase, increased nuchal translucency
  • Quadruple blood screening test: AFP decreased, hCG increased, inhibin A increases
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84
Q

What is Edwards syndrome?

A

Trisomy 18

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85
Q

What is trisomy 18 called?

A

Edwards syndrome

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86
Q

What are some symptoms of Edward’s syndrome?

A
  • Small chin
  • Clenched hands with overlapping fingers
  • Malformations of heart, kidney and other organs
  • If people survive the first year, generally have profound LD
    Babies will have severe intellectual disability and a failure to thrive.
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87
Q

What is Patua syndrome?

A

Trisomy 13

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88
Q

What is trisomy 13 called?

A

Patau syndrome

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89
Q

What are some symtpoms of Patau syndrome?

A

Like Edward’s syndrome, approximately only 10% survive the first year, generally with profound LD. About 50% die within 1 month.
Congenital heart disease is usual.

Symptoms:

  • Cleft lip and palate
  • Microphthalmia
  • Abnormal ears
  • Clenched fists
  • Post-axial polydactyly (extra linger finger)
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90
Q

What is the most common mutation of a trisomy?

A

These trisomies all usually arise from maternal non-disjunction (failure of normal separation of the two-chromosome number 21, 18 or 13) in meiosis.
Trisomies more frequent with increase maternal age.

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91
Q

What percentage of the genome is coding?

A

1.5%

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92
Q

Most of the genome is inter-genic, what is the meaning of this?

A

Most of the genome is inter-genic. An Intergenic region (IGR) is a stretch of DNA sequences located between genes. Intergenic regions are a subset of noncoding DNA. Occasionally some intergenic DNA acts to control genes nearby, but most of it has no currently known function.

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93
Q

What does sub-microscopic mean?

A

Too small to see under light microscope

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94
Q

What is an aneuploidy?

A

This is an abnormal number of chromosomes. The number is not a multiple of 23.

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95
Q

What is a point mutation?

A

This is a mutation that affects a single nucleotide. Point mutations most commonly involve the substitution of one base for another (which changes the complementary base as well in DNA). The term point mutation also includes insertions or deletions of a single base pair.

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96
Q

DNA sequencing is used for analysing point mutations. Does this technique work with known or unknown mutation locations?

A

Unknown

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97
Q

What are the two types of DNA sequencing?

A 
Sanger: one gene at a time
Massively parallel (next generation): many genes at once
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98
Q

What is sanger sequencing?

A

A type of DNA sequence (unknown mutation location) that analyses one gene at a time

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99
Q

What is next generation sequencing?

A

A type of DNA sequence (unknown mutation location) that analyses many genes at a time

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100
Q

What type of DNA sequencing analysis many genes at once?

A

Massively parallel

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101
Q

What type of DNA sequencing analyses one genes at once?

A

Sanger

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102
Q

What is Allel-specific PCR (ARMS)>

A

Special PCR that analyses only specific known point mutations. For example in cystic fibrosis where the specific mutation is usually known.

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103
Q

ARMS is used for analysing point mutations. Does this technique work with known or unknown mutation locations?

A

Known location

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104
Q

What are the two types of sub-microscopic detection techniques?

A
  • MLPA (PCR method)

- Chromosomal micro-array (CMA)

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105
Q

Describe MLPA

A

This is a technique for analysing sub-microscopic mutations in a known chromosome location.

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106
Q

Describe chromosomal micro-array

A

This is a technique for analysing sub-microscopic mutations in a unknown chromosome location.

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107
Q

What is the technique to analyse aneuploidy?

A

QF-PCR

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108
Q

What is the best technique to analyses aneuploidy?

A

QF-PCR

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109
Q

What is the function to QR-PCR?

A

Analyses aneuploidy

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110
Q

What is karyotyping and FISH for?

A

Whole chromosome anaylsis

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111
Q

Describe the process from DNA to a VCF file

A
  • DNA
  • massively parallel sequencing
  • sequence alignment
  • BAM file
  • Variant calling (identification)
  • VCF file
    Then there is date filtering step (e.g. removing common variants).
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112
Q

What gene is affected in Spinocerebellar ataxias?

A

ATXN gene. This gives instructions for making Ataxin protein.

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113
Q

What is the mutation in Spinocerebellar ataxias?

A

There is abnormal repetition of CAG.

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114
Q

is familiar breast cancer dominant or recessive?

A

Dominant

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115
Q

What is the function of the BRCA gene?

A

Involved in double-stranded DNA repair

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116
Q

What two main cancers are associated with the BRCA gene?

A

Breast and Ovarian

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117
Q

What is the main cancer is HNPCC (Lynch syndrome)?

A

Colorectal

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118
Q

Is HNPCC dominant or recessive?

A

Dominant

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119
Q

What other cancer is associated with HNPCC?

A

Endometrial
Ovarian
Hepatobiliary
Urinary tract

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120
Q

What are the main responsible genes in HNPCC?

A
  • MSH2

- MLH1

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121
Q

What are the functions of MSH2 and MLH1?

A

DNA mismatch repair

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122
Q

What is the main cancer in MuTYH (MAP)?

A

Colorectal

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123
Q

Is MAP dominant or recessive?

A

Recessive

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124
Q

What is the responsible gene in MAP?

A

MUTYH

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125
Q

What is the function of MUTYH?

A

DNA glycosylase required for base excision repair

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126
Q

What is the gene mutated in LI-Fraumeni syndrome?

A

TP53

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127
Q

What is the main cancer is Li-Fraumeni syndrome?

A

Sarcoma and Breast cancer

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128
Q

Is Li-Fraumeni dominant or recessive?

A

Dominant

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129
Q

What is the gene responsible for Cowden syndrome?

A

PTEN

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130
Q

What does a mutation in PTEN cause?

A

Cowden syndrome

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131
Q

What does a mutation in MSH2 or MLH1 cause?

A

HNPCC

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132
Q

How many tumour suppressor gens have been discovered?

A

90

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133
Q

What are some roles of tumour suppressor genes?

A
  • negatively relate cell cycle control
  • promote apoptosis
  • play a role in cell adhesion
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134
Q

Does a mutation in TSGs cause a loss or gain in function?

A

Loss in function

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135
Q

Describe the two-hit hypothesis

A

When an individual inherits a mutated copy of a Tumour suppressor gene, the other normal copy of the gene would otherwise still function sufficiently to prevent oncogenesis. Therefore, for cancer to develop, the other allele must be inactivated.
This is known as the ‘two hit hypotheses’.
As the second hit involves the loss of the remaining gene copy through deletion or recombination, tumour DNA will often show loss of heterozygosity.

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136
Q

Give some examples of tumour suppressor genes

A
  • Rb1
  • P53
  • MLHE
  • BRCA
  • APC
  • MSH2
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137
Q

Is BRCA a tumoru supressor gene?

A

Yes

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138
Q

A patient with Li-Fraumeni syndrome, what is the risk of getting cancer by age 50?

A

90%

- common ones include breast, brain, adrenal, pancreas, stomach

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139
Q

Does a mutation in a proto-oncogene cause a loss or Gian in function?

A

Gain in function

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140
Q

What are some examples of photo-oncogenes?

A
  • c-MYC
  • Ras
  • RET
  • MET
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141
Q

How many photo-oncogenes need to be mutated for cancer to develop?

A

Genetic alteration of one, rather than both, allele is sufficient to confer a tumorigenic effect on the cell possessing it.

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142
Q

What percentage of breast cancer is due to the familiar kind?

A

5-10%

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143
Q

What are the four types of gens that can cause breast cancer?

A

Familial breast cancer is due to mutations in the BRCA1 or the BRAC2 gene. A small minority is due to Li-Fraumeni (P53) syndrome and Cowden syndrome (PTEN). In recent years, there has been a link with PALB2 gene causing increased risk of Breast cancer.

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144
Q

When should familiar breast cancer be suspected?

A
  • early onset (<40 years)
  • bilateral disease
  • co-excistant ovarian cancer
  • family history
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145
Q

What are the four types of gens that can cause ovarian cancer?

A
  • BRCA1
  • BRCA2
  • MLH1
  • MSH2
    MSH and MLH are correlated with endometrial and colorectal cancer.
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146
Q

Screening is relatively easy in breast cancer. it is the same with ovarian?

A

No

147
Q

Which mutation, BRCA1 or BRCA2, give a increased risk of developing a wider range of tumours>

A

Carries of the BRCA2 mutation are at increased risk of developing a wider range of tumours than BRCA1 mutation carriers. Examples include malignant melanomas, prostate, pancreatic, gall-bladder and bile duct.

148
Q

What tumours, in addition to breast and ovarian, are carriers of the mutated form of BRCA2 at increased risk of?

A 
Melanomas
Prostate
Pancreatic
Gall-Bladder
Bile duct
149
Q

What gens play a role in double DNA break repair?

A

BRCA1 and BRCA2
The most important role for BRCA1 and BRCA1 in maintenance of genomic integrity. This is achieved by their role in DNA double-strand break repair, known as homologous recombination.
Homologous recombination is a type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of DNA.

150
Q

What type of analysis is used for BRCA1 and BRCA2?

A

Mutations in these genes is analysed by DNA sequencing, next generation screening.

151
Q

What percentage does a mastectomies reduce the risk of Brest cancer by?

A

90%

152
Q

What gene is associated with male breast cancer?

A

BRCA2

153
Q

Can incomplete penetrance be seen with BRCA1 and BRCA2 mutations?

A

Incomplete penetrance can be seen in BRCA1 and BRCA2 genes. If an individual inherits a faulty copy of the BRCA gene, the chance of getting breast cancer is only 80%.

154
Q

What is the Breast cancer risk of BRAC1 mutation?

A

40-87%

155
Q

What is the ovarian cancer risk of BRAC1 mutation?

A

22-65%

156
Q

What is the Breast cancer risk of BRAC2 mutation?

A

18-88%

157
Q

What is the ovarian cancer risk of BRAC2 mutation?

A

10-35%

158
Q

What percentage of colorectal caner is due to genetic susceptibility?

A

5-10%

159
Q

What are two examples of dominant conditions that cause colorectal cancer?

A

Most dominant conditions are due to HNPCC (hereditary non-polyposis colon cancer), also known as Lynch syndrome and Familial adenomatous polyposis (FAP).

160
Q

What is an of a recessive conditions that cause colorectal cancer?

A

An example of a recessive condition is MUTYH-associated polyposis (MAP).

161
Q

What gene is mutated in FAP?

A

APC - causing a over activation of WNT signalling

162
Q

What condition does a mutation in APV cause?

A

FAP

163
Q

How early on will bowel screening be offered with someone with FAP?

A

From age 11.

- due to risk of any polpys developing in the teens year turning malignant.

164
Q

When is inherited colon cancer suspected?

A

Inherited colon cancer is suspected if there are many polyps present early age onset or multifocal cancer, family history or related caner such as endometrial cancer.

165
Q

How many polyps are usually present in HNPCC?

A

10

166
Q

How many polyps are usually present in FAP?

A

100

167
Q

In addition to MSH2 and MLH1 mutations causing HNPCC, what other mutated genes can cause this?

A

MSH6

PMS2

168
Q

Males who have a mutation for HNPCC gens have a what percentage risk of developing colon cancer?

A

80-90%

169
Q

Females who have a mutation for HNPCC gens have a what percentage risk of developing colon cancer?

A

40%

170
Q

Females who have a mutation for HNPCC gens have a what percentage risk of developing endometrial cancer?

A

5%

171
Q

How often are colonoscopies done for when there is HNPCC mutations?

A

2 yearly colonoscopies from the age of 25 and 2 yearly upper GI from 50

172
Q

What type of protein is P53?

A

Intracellular transcription factor

173
Q

What is consanguinity a sign of?

A

Autosoma recessive conditions

174
Q

What mutation can stillbirths and miscarriages show a sign of?

A

Chromosomal rearrangement

175
Q

What gene is mutated in Cowden syndrome?

A

PTEN

176
Q

What is polydactylyl?

A

Extra fingers or toes

177
Q

What is the name for extra fingers or toes?

A

Polydactlyly

178
Q

What is syndactlyly?

A

Finger/toes joined together

179
Q

What name describes fingers/toes joined together?

A

Syndactylyl

180
Q

What is hypertelorism?

A

This is where the pupils are too far apart

181
Q

What name describes the condition where pupils are oo far apart?

A

hypertelorism

182
Q

What is an example of a condition with brand toes?

A

Rubinstein Tayble syndrome

183
Q

When is Chorionic villus sampling varied out?

A

First trimester

184
Q

Where is a Chorionic villus sampling taken from?

A

Chorionic villus sampling takes a sample of chorionic Villi from the placenta.

185
Q

When is amniocentesis carried out?

A

Second trimester

186
Q

What is Pre-Implantation diagnosis?

A

This is where one or two cells are removed for testing, at three days when the embryo contains 6-10 cells (blastomere). The cells are tested for any possible mutations.
This procedure costs thousands to carry out. Because the embryos need tested, IVF needs to be carried out. Embryos which have been tested and free of the conditions will be placed into the womb.

187
Q

How many cells are removed in PGD?

A

One or two

188
Q

When are cells removed for PGD?

A

When the embryo contains 6-10 cells (blastomere stage).

189
Q

When the cells are collected for PGD, what techniques are used for analysis?

A

FISH or QF-PCR

190
Q

Describe trophectoderm biopsy

A

This is a test that uses an oder embryo. There are around 100 cells in the embryo (trophectoderm).

191
Q

What are some pros of a PGD?

A
  • permits implantation of unaffected embryos

- termination pregnancy is then unnecessary

192
Q

What are some cons of a PGD?

A
  • possible long wait
  • not available for all women ( may restrict by age or by AMH level as an indicatory of number of refined follicles)
  • difficulty with multiple visits and procedures
193
Q

For testing, what colour is an X chromosome?

A

Green

194
Q

For testing, what colour is an Y chromosome?

A

Red

195
Q

What is the success rate of PGD?

A

1 in 3 pregnancies will advance to term.

196
Q

What three stages of life are genetic screening programmes offered at?

A
  • pregnancy
  • neonatally
  • adulthood
197
Q

What are some criteria for screening programmes?

A
  • Should be clearly defied disorder
  • With appreciable frequency
  • Advantage to early diagnosis
  • Few false positives (specificity)
  • Few false negatives (sensitivity)
  • Benefits outweigh the costs
  • Condition should be an important health problem
  • All cost effective primary prevention interventions should have been implemented
  • Simple, safe, precise and validated screening test
  • Recognised treatment
  • Benefit gained by individuals from screening programmes outweighs harms
198
Q

Is nuchal translucency raising or decreased in Down syndrome?

A

Increased

199
Q

What is mass spectrometry and what are some conditions that can be screening for in neonates?

A

Phenylketonuria and MCADD

- uses ionisation techniques

200
Q

What is immune-assassy and what are some conditions that can be screening for in neonates?

A

Looking for antibodies. Examples include congenital hypothyroidism and cystic fibrosis.

201
Q

What condition can be tested for in HPLP in neonates?

A

Sickle cell disorder

202
Q

What are some examples of postnantel screening genetic tests?

A
  • Tay Sachs screening for Jewish people

- Thalassaemia for people at risk

203
Q

What does a double line show in a pedigree?

A

The parents are related

204
Q

What gene proportion does a mother and son have in common?

A

50%

205
Q

What gene proportion do two first cousins have in common?

A

1/8 (12.5%)

206
Q

What gene proportion does a brother and sister have in common?

A

50% (on average)

207
Q

What gene proportion does a boy and his uncle have in common?

A

25%

208
Q

What is the miscarriage rate in chorionic villous sampling?

A

1 in 50

209
Q

What is the miscarriage rate in amniocentesis?

A

1 in 100

210
Q

What is Turner’s syndrome?

A

This is where a girl has only one normal X chromosome. Hence there are only 45 chromosomes.

211
Q

What is Klinefleter’s syndrome?

A

This is where there is a chromosome arrangement of XXY (47 chromosomes)

212
Q

What is sensitivity?

A

The ability of a test to correctly identify those people with the disease

213
Q

What is specificity?

A

The ability of a test to correctly identify people without the disease

214
Q

What describe the ability of a test to correctly identify people with the disease?

A

Sensitivity

215
Q

What describe the ability of a test to correctly identify people without the disease?

A

Specificity

216
Q

How is Specificity calculated?

A

TN/(TN+FP)

217
Q

How is sensitivity calculated?

A

TP/(TP+FN)

218
Q

What does the following calculation give: TN/(TN+FP)?

A

Specificty

219
Q

What does the following calculation give: TP/(TP+FN)?

A

Sensitivity

220
Q

What would a the chance of a granddaughter of an obligate carrier in an x-linked recessive condition being a carrier?

A

25%

221
Q

If there are two different gene mutations on the same copy of a gene, would this be enough to cause an autosomal recessive disorder?

A

No. Two mutations would make the gene extra faulty but the other gene would be normal.

222
Q

Could a female be affected by an x-liked recessive disorder if both oh her x-chromosomes were affected?

A

Yes

223
Q

A boy hass cystic fibrosis. What is the chance of his uncle having the disorder?

A

50%

224
Q

A boy hass cystic fibrosis. What is the chance of his older sister having the disorder?

A

67%

225
Q

MLPA is most commonly used to detect what?

A

Used to detect deletion of a gene when there is a known position. BRCA will usually have a point mutation.

226
Q

What is QF-PCR usually used for?

A

Trisomy 21, 18 or 13

227
Q

What is ARMS used for?

A

Single nucleated substitution in known position in a gene

228
Q

Does NF1 have genetic anticipation?

A

No

229
Q

Does spinocerebellar dystrophy have genetic anticipation?

A

Yes

230
Q

What way does DNA rotate?

A

Clockwise

231
Q

What are the base pairs in DNA?

A

AT

CG

232
Q

How many hydrogen bonds are between A and T in DNA?

A

2

233
Q

How many hydrogen bonds are between C and G in DNA?

A

3

234
Q

Does DNA methylation increase or decrease expression?

A

Decrease

235
Q

What are the three stop codons?

A
  • TAA
  • TAG
  • TGA
236
Q

Can a man marry mutations in BRCA1 and BRCA2?

A

Yes

237
Q

Is TAA a stop codon?

A

Yes

238
Q

Is TAG a stop codon?

A

Yes

239
Q

Is TGA a stop codon?

A

Yes

240
Q

What carriers out transcription?

A

RNA polymerase

241
Q

What carriers out DAN replication?

A

DNA polymerase

242
Q

Is sickle cell disease dominant or recessive?

A

Autosomal recessive

243
Q

Is MYC a proto-oncogene or tumour recessive gene?

A

Proto-oncogene

244
Q

Which chromosome is shorter; X or Y?

A

Y

245
Q

What is precision medicine?

A

Precision medicine: is an approach to patient care that allows doctors to select treatments that are most likely to help patients based on a genetic understanding of their disease. This may also be called personalized medicine.

246
Q

What test is involved in non-invasive prenatal diagnosis?

A

Blood test

247
Q

What is a variant of uncertain significance?

A

A Variants of uncertain significance is a variant form of a gene, which has been identified through genetic testing, but whose significance to the function of health of an organism is not known.

248
Q

Ivacaftor is a drug for Cystic fibrosis. Describe the mechanism of action

A

G551D is the third most common CF mutation in Cystic fibrosis. This causes the CTFR channel to blocked. Ivacaftor re-opens this channel.

249
Q

What is the mechanism of action of Gefitinib?

A

This inhibit EGFR (lung cancer mutation)

250
Q

Why is exon skipping used in DMD?

A

Exon skipping can be used in DMD to convert DMD to BMD by altering the splicing patterns. This done with antisense oligonucleotides.

251
Q

Describe gene editing with the CRISPR-CAS9 system

A

These technologies allow genetic material to be added, removed, or altered at particular locations in the genome.
In the lab, a small piece of RNA with a short guide sequence that attaches to a specific target sequence of DNA in a genome. The RNA also binds to the Cas9 enzyme. This enzyme allows DNA to be cut, hence removing unwanted material.

252
Q

Describe gene silencing in Hutington’s

A

Gene Silencing: Antisense oligonucleotides (ASOs) and RNA-interference (RNAi)-based therapies work by binding specifically to faulty RNA sequences that are made from mutated HTT gene codes.

  • An antisense oligonucleotide: binding and marking HTT mRNA for destruction
    • RNAi-based therapies: incorporated into the naturally occurring gene-silencing proteins present in the body before being able to target the mutated RNA sequence
253
Q

Describe the drug therapy ‘increasing expansion’ in spinal muscular atrophy with the drug Spinraza

A

A drug called Spinraza, contains an allele-specific anti-sense oligonucleotide, which controls mutations caused in a chromosome. The selectively binds and targets RNA and regulate gene expression. It enhances the amount of functional SMN protein. It has a role in spinal muscular atrophy.

254
Q

Describe the drug therapy ‘exon skipping’ ?

A

The process of exon skipping involves the process of skipping an exon. Small pieces of DNA called antisense oligonucleotides are used to mask the exon you want to skip, so that it is ignored during protien production.

255
Q

Describe DNA replication

A

Each strand separates at a number of points (by the action of DNA helicase) and each strand severs as a template upon which the missing partner can be reconstructed by base paring with free nucleotides.

A RNA primer will bind to the 3’ end to allow DNA polymerase to add free nucleotides.

The nucleotides are brought together by the action of the DNA-dependent DNA polymerases alpha and beta and are hydrogen bonded to the template stand.

A primer is needed to start replication.
1. Leading strand is synthesised continuously. DNA polymerase adds nucleotides to the deoxyribose (3’) ended strand in a 5’ to 3’ direction.
2. Lagging strand is synthesised in fragments. Nucleotides cannot be added to the phosphate (5’) end because DNA polymerase can only add DNA nucleotides in a 5’ to 3’ direction. The lagging strand is therefore synthesised in fragments. The fragments are then sealed together by an enzyme called ligase.
Replication proceeds in both directions from each initiation point until the new strands of DNA are complete.

256
Q

Describe the transcription phase of protein synthesis

A

Gene expression begins with the process called transcription, which is the synthesis of a strand of mRNA. The DNA unwinds and the two strands separate.
There are three stages of transcription:
- Initiation: a region at the beginning of the gene called a promoter triggers start of transcription
- Elongation: RNA polymerase unwinds the DNA segment and creates a new strand of called mRNA
- Termination: there is a stop codon that triggers the enzyme to terminate and release the mRNA transcript

The mRNA strand undergoes splicing, whereby the non-coding regions (introns) are removed by a spliceosome.

Translation is the process of synthesizing a chain of amino acids called a polypeptide.

257
Q

What is gonadal mosaicism?

A

Gonadal mosaicism is where some of a person’s germ cells (egg or sperm) are normal and some contain a specific genetic alteration or chromosome problem. It cannot be tested on a blood test.

258
Q

Describe up slanting palpebral tissues

A

This is where the medial corner of the eye is lower down than the lateral corner. It is seen in Down syndrome.

259
Q

Describe down slanting setting palpebral tissues

A

This is where the medial corner of the eye is high up than the lateral corner. This is seen in Marfan’s syndrome.

260
Q

What is a multifactorial conditions and can you give an example?

A

Multifactorial is where there is the involvement of a number of factors, especially genetic an environmental factors. Mc-Cune-Albright syndrome is typically regarded as occurring asa result of a mutation in a single gene.

261
Q

What is PCR used for in PGD?

A

Detect specific mutations or haplotype

262
Q

What is FISH used for in PGD?

A

Detect an unbalanced chromosome abnormality

263
Q

Is there detail sex determination of embryos in sex-linked diseases in PGD?

A

Yes

264
Q

How many base pairs does the human genome contain?

A

3.2 thousand million

265
Q

True or false: the human genome contains 3 million base pairs

A

FALSE:

the human genome contains 3.2 thousand million base pairs

266
Q

What are the pyrimidine bases ?

A

Cytosine and Thymine

267
Q

Does the sugar-phosphate backbone of the DNA molecule depend on covalent or hydrogen bonding?

A

Covalent

268
Q

What causes an increase in new mutations: maternal age or paternal age

A

Paternal

269
Q

Is male-male transmits see in X-linked conditions?

A

No

270
Q

If man with autosomal recessive albinism has a child with a carrier of the same condition, what is the chance of the child being affected?

A

50%

271
Q

What is the proportion.of genes in common between a women and her great grandmother?

A

1/16

272
Q

What is the proportion.of genes in common between two first cousins?

A

12.5%

273
Q

Is MLH1 a tumour suppressor gene or a proto-oncogene?

A

Tumour Suppressor gene

274
Q

What is the chance of a daughter of someone who has the autosomal dominant breast cancer (BRAC)?

A

The chance getting breast cancer is 40%. Her risk of getting the gene from her mother is 50% but the chance of her developing breast cancer is 80%.

275
Q

What are modifier genes?

A

Modifier genes are genetic variants that can affect the manifestation of a disorder. For example, the chance of someone developing breast cancer with a BRCA mutation is influenced by the absence/presence of FGFR2.

276
Q

What cancer of the adrenal gland is associated with NF1?

A

Pheochromocytomas

277
Q

What population is offered Tay Sachs disease screening?

A

Jewish population

278
Q

What is genetic heterogeneity?

A

Different mutations giving a similar or the same phenotype

279
Q

What is the carrier frequency of cystic fibrosis?

A

1 in 25

280
Q

What gene is mutated in cystic fibrosis?

A

CFTR

281
Q

What will sweat show in cystic fibrosis?

A

Increased sodium and chloride concentration

282
Q

What is hypertelorism?

A

This is where the body organs are too far apart

283
Q

What is syndactyly?

A

This is where the digits are joined

284
Q

When is chorionic villus sampling carried out?

A

First trimester

285
Q

When is amniocentesis carried out?

A

Second trimester

286
Q

What is the miscarriage risk for chorionic villus sampling?

A

1/50

287
Q

What is the miscarriage risk for amniocentesis?

A

1/100

288
Q

What is sensitivity?

A

This is the ability of. test to correctly identify people with the disease

289
Q

What is specificity?

A

The ability of a test to correctly identify people without the disease

290
Q

Is Huntingtons autosomal dominant?

A

Yes

291
Q

What does CAG code for?

A

Glutamine

292
Q

Does Huntingtons have genetic anticipation?

A

Yes

293
Q

Is myotonic dystrophy dominant?

A

Yes

294
Q

What are some symtpoms of myotonic dystrophy?

A
  • progressive muscle weakness
  • myotonia
  • cataracts
  • increased susceptibility for diabetes
295
Q

What is the mutation in myotonic dystrophy?

A

There is a mutation in the CTG gene in the 3’ downstream area (transcribed but not translated area) in the DMPK gene.

296
Q

What is the testing for cystic fibrosis?

A

IRT will be measured and will be abnormal in CF patients. If the child is detected to have this, it will be confirmed with DNA testing. There will be increase chlorine in the sweat.

297
Q

Will neurofibromatosis type one have cafe au laities macules?

A

Yes

298
Q

What are lisch nodules?

A

These are sign in neurofibromatosis type one and they are brown mounds on the iris.

299
Q

Can you use PDE-5 inhibitors in hypotension?

A

No

300
Q

Can you use PDE-5 inhibitors in unstable angina?

A

No

301
Q

When should viagra be taken?

A

One hour before sexual activity

302
Q

What are some common side effects of viagra?

A

Backpain, dyspepsia, flushing, migraine, nasal congestion

303
Q

What is the inheritance of Lynch syndrome?

A

Autosomal dominant

304
Q

What is the function of MSH2 and MH1?

A

DNA mismatch repair

305
Q

What is the inheritance of MuTYH?

A

AR

306
Q

What is the function of MuTYH?

A

Base excision repair

307
Q

What cancer does Li-Fraumenic syndrome increase the risk of?

A

Sarcoma and Breast cancer

308
Q

What cancer risk does Cowden syndrome increase the risk of?

A

Breast and Thyroid

309
Q

Is Rb1 a tumour suppressor?

A

Yes

310
Q

Is P53 a tumour suppressor?

A

Yes

311
Q

Is RAS a oncogene?

A

Yes

312
Q

Is RET an oncogene?

A

Yes

313
Q

When should familiar breast cancer be suspected?

A

This should be suspected when there is an early onset (<40), bilateral disease, family history and ovarian cancer.

314
Q

What is mutated in FAP?

A

The APC gene (causing over activation of WNT signalling)

315
Q

Do mitochondria have introns?

A

No

316
Q

What is the shape of mitochondrial genetic mitral?

A

Circular

317
Q

Does Huntington’s have complete penetrance?

A

Yes

318
Q

What is compound heterozygous?

A

This is where there is the presence of two mutated alleles at a particular gene

319
Q

What is double heterozygous?

A

This is where there is the presence of two different mutation on different genes.

320
Q

What are some examples x-linked dominant conditions?

A
  • Rett syndrome
  • Incomtinentia pigment
  • vitamin resistant rickets
321
Q

How many genes do mitochondria have?

A

37 genes

322
Q

What is an example of disease with mitochondria inheritane?

A

Leigh’s disease

323
Q

Is NF1 dominant?

A

Yes

324
Q

Is there macrocephaly in NF1?

A

Yes

325
Q

Is there short stature in NF1?

A

Yes

326
Q

What are some complications of NF1?

A
  • hypertension
  • scoliosis
  • pathology tibial fractures
  • significant tumours: pheochromocytoma
  • mild learning difficulties
327
Q

What is the mutation in Fragile x-syndrome?

A

UTR

328
Q

What is the dosing for Viagra

A

The dose is 50mg, to be taken one hour before sexual activity. Effects may last 4-5 hours. The maximum dose is 100mg.

329
Q

What is the dosing for Tadalafil?

A

There is 10mg taken 30 minutes before sex. This may last 36 hours.

330
Q

What is the dosing for Vardenafil?

A

10mg is taken as needed, 25 minutes before sex. The effects may last 4-5 hours.

331
Q

What is the dosing for Avanafil?

A

100mg is taken 15 minutes before sex and it may last unto 6 hours.

332
Q

What conditions can show up slanting palpebral fissures?

A

Down syndrome

333
Q

What colour is the X chromosome?

A

Green

334
Q

What colour is the Y chromosome?

A

Red

335
Q

What is sensitivity?

A

This I the ability of a test to correctly identify people with the condition. These is calculated by (TP)/(TP+FN)

336
Q

What is specificity?

A

This is the ability of a test to correctly identify people without the disease. This is calculated by TN/(TN+FP)

337
Q

What does CAG code for?

A

Glutamine

338
Q

What are some features of NF1

A

-short stature
- macrocephaly
- cafe au lait macules
- neurofibromas
- lisch nodules
There is variable expressivity. Complications include hypertension, mild cognitive impairment, pheochromocytoma and pathological tibial fracture.

339
Q

Inheritance by MERRF is by what mechanism?

A

Mitochondrial

340
Q

Inheritance by achondroplasia is by what mechanism?

A

Autosomal dominant

341
Q

Inheritance by haemophilia B is done by what mechanism?

A

X-linked

342
Q

Inheritance by Marfan’s is done by what mechanism?

A

Autosomal dominant

343
Q

Inheritance by MELAS is done by what mechanism?

A

Mitochondrial

344
Q

Inheritance by tay Sachs is done by what mechanism?

A

Autosomal recessive

345
Q

Inheritance by congenital adrenal hyperplasia is done by what mechanism?

A

Autosomal recessive

346
Q

Inheritance by congenital adrenal hypoplasia is done by what mechanism?

A

X-linked

347
Q

Inheritance by MODY is done by what mechanism?

A

Dominant

348
Q

What are some initial symptoms of Huntington’s?

A
  • incoordination
  • depression
  • irritability
349
Q

What chromosome is the Huntington gene located on?

A

Chromosome Four

350
Q

What is Myotonia?

A

Prolonged contraction of a muscle

351
Q

Is there meconium ileus in neonates with cystic fibrosis?

A

Yes

352
Q

How can lisch nodules on the iris by examined?

A

Slit lamp

353
Q

What is the largest human gene?

A

DMD (this codes for dystrophin gene).

354
Q

How long does PCR take?

A

2-3 hours

355
Q

What stage are eggs taken out for PGD?

A

Blastomere

356
Q

What are some exmaples of conditions looked for in the neonatal heel prick test?

A
  • cystic fibrosis
  • sickle cell disease
  • congenital hypothyroidism
  • phenylketponuria
357
Q

What are some investigations for erectile dysfuction?

A
  • general examination: any anatomical?
  • Glucose
  • Blood pressure
  • HbA1c
  • Cholesterol
  • Testosterone (8am and 11am), FSH, LH, Prolactin
  • Thyroid
  • LFTs and U&Es
    PSA and prostate exam should be done if the patient is over 50.
358
Q

Does autosomlal dominant or recessive have variable expressivity?

A

Autosomal dominant

359
Q

What is gonadal mosaicism

A

gonadal mosaicism (mutation
might be in more than one egg or
sperm cell in the parent’s gonads)

360
Q

What is MLPA used to detect?

A

Deletion of a gene

361
Q

What are some drug interactions with cGMP-specific PDE5 inhibitors?

A 
Nitrates (CI)
Guanylate cyclase stimulators (CI)
Alpha- Blockers
Cytochrome P450 inhibitor and inducer drugs eg clarithromycin, rifampicin
(check BNF for full list of drugs)
Grapefruit juice
362
Q

What are some common side effects of Viagra?

A
  • headache
  • flushing
  • backpain
  • nasal congestion
  • vomiting
363
Q

What is the second line drug treatment for erectile dysfuciton?

A

synthetic prostaglandin E1 analogue- alprostadil.

Genetics (3 decks)

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