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IMMS > Genetics > Flashcards

Genetics Flashcards

1
Q

What percentage of common cancers are due to underlying genetic predisposition?

A

5%

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2
Q

Out of autosomes 1 - 22, which is shortest, which is longest?

A

1 is longest, 22 is shortest

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3
Q

What letters represent short arm and long arm?

A

q represents long arm, p represents short r
arm which are separated by the centromere

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4
Q

What are 5 types of chromosomal abnormalities?

A

Deletion - section missing
Duplication - section copied
Whole extra chromosome
Whole chromosome missing
Translocation - Sections move between chromosomes

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5
Q

What causes down syndrome?

A

Trisomy on chromosome 21 (extra chromosome)

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6
Q

What are the 2 types of translocation?

A

Balanced - No loss of genetic material therefore healthy person
Unbalanced - Loss or gain of genetic material potentially causing human disease

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7
Q

What are the 3 genomes?

A

Germline - Genome in sperm or egg/ heritable
Somatic - Genome found in every other tissue/ not heritable
Mitochondrial - Found only in mitochondria/ heritable

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8
Q

How is a recessive disease carrier shown on a pedigree diagram?

A

Half shaded circle or square or a black dot

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9
Q

What is mutagenesis?

A

Alteration to the genomic code by exposure to substance (mutagens) in the womb or postnatal

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10
Q

What is teratogenesis?

A

Damaging effect on embryonic and fetal development by exposure to a substance (teratogens)

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11
Q

What are some examples of teratogenesis?

A

Virus-causing cell death - Certain viral infections can harm developing cells causing issues in growth and function
Toxin interrupting blood supply - Certain toxins can interfere with the bloodstream to developing tissues

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12
Q

Can some teratogens act as mutagens?

A

Yes, some cause changes to the DNA in cells: if a pregnant lady was taking thalidomide or exposed to ionising radiation

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13
Q

What are 2 types of malformation?

A

Major and minor

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14
Q

When are the malformations considered to be due to genetics?

A

When there are more than two minor malformations or when there are major malformations

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15
Q

What would you do if a child had 2 visible minor malformations?

A

A thorough examination as more minor malformations could suggest an underlying genetic condition

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16
Q

What does dosage sensitive mean?

A

2 copies are required to be healthy, if there are more or less issues can arise

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17
Q

What is an example of a dosage sensitive disease?

A

Sonic hedgehog (Shh) in limb development, precise levels are crucial as too much or too little disrupt normal development

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18
Q

Which chromosomes are Robertsonian?

A

13, 14, 15 and 21

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19
Q

Why are Robertsonian chromosomes predisposed to translocations between one another?

A

Short arms fuse to create 1 long-arm chromosome, with no caps on chromosome ends so more susceptible to translocation movements

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20
Q

What is penetrance?

A

Percentage of individuals who have variants in certain genes who develop medical conditions due to it (not all people with variants develop the linked conditions)

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21
Q

What is recurrence risk? (Autosomal dominant)

A

Affected person has a 50% chance of having an affected child

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22
Q

What is age-related penetrance?

A

The likelihood that a genetic mutation will manifest as a disease or trait due to increasing age

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23
Q

What is variable expressibility?

A

People with the same gene variant can have a wide range of symptoms or physical features

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24
Q

What are De novo mutations?

A

Genetic alterations that aren’t inherited by parents occur during gamete formation or in the early stages of embryonic development

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25
Q

Why are De novo mutations more common with age?

A

More common in ageing males as the stem cells don’t copy DNA as accurately, relatively stable over a female lifetime

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26
Q

Why do consanguineous relationships increase likelihood of genetic mutations?

A

As both parents are blood-related, they may be carrying the recessive allele(s) for the same genetic condition

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27
Q

What is the carrier risk of cystic fibrosis?

A

1/25

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28
Q

What is the carrier risk for haemochromatosis?

A

1/10

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29
Q

What is the carrier risk for congenital adrenal hyperplasia?

A

1/35

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30
Q

What is cystic fibrosis?

A

Genetic conditions causing the production of thick, sticky mucus which can lead to blockages, damage or infections in the lungs or digestive system

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31
Q

What is haemochromatosis?

A

Where iron levels in the body slowly build up over time

32
Q

What is congenital adrenal hyperplasia?

A

Adrenal glands don’t produce enough cortisol, potentially causing early puberty, rapid growth during childhood but short stature, acne and irregular menstrual periods in females

33
Q

What is X-linked inheritance?

A

The pattern of inheritance for chromosomes located on the X chromosome

34
Q

How are males impacted by X-linked recessive conditions?

A

If males have the recessive allele, they will have the condition as they only have 1 X chromosome. If they have the dominant allele, they won’t have the condition.

35
Q

How are females impacted by X-linked recessive conditions?

A

Females require both alleles to be recessive to be affected by the condition as they have 2 X chromosomes. If they are heterozygous or homozygous dominant, they will be unaffected. However, if they are heterozygous, they will be carriers of the condition.

36
Q

How are males and females affected in X-linked dominant conditions?

A

Both males and females are affected equally

37
Q

What is male to male transmission?

A

An affected man has an affected son

38
Q

Can the condition be X-linked if male to male transmission occurs?

A

No as sons get their Y chromosome from their father so any affected genes on the X chromosome have to be from the mother

39
Q

What is Duchenne muscular dystrophy?

A

Mutation in dystrophin gene on X-chromosome causing absence of dystrophin protein in skeletal muscle (X-linked recessive)

40
Q

What does a person with Duchenne muscular dystrophy experience?

A

Limb weakness and eventually resulting in wheelchair use

41
Q

Why is DMD more prevalent in males compared to females?

A

It is very uncommon for both female X chromosomes to mutate compared to just the 1 for males

42
Q

What is germline mosaicism?

A

Mutation in germline (sex) cells causing DNA to differ from somatic (rest of body) cells

43
Q

What can germline mosaicism cause?

A

A parent with no affected gene on blood test to pass on X-recessive conditions as only sex cells affected

44
Q

What is gonadal mosaicism?

A

Mutations only found in the ovary and not in the blood of the DNA mother

45
Q

Can you test for germline mosaicism?

A

No clinical tests, it is only possible to do prenatal tests (amniocentesis) to check whether the child has the conditions

46
Q

What is lyonisation?

A

Random inactivation of the X chromosome (only in females)

47
Q

What are some potential concerns with lyonisation?

A

If a healthy X-chromosome is inactivated more than the mutated X-chromosome, it will cause disease

48
Q

What is skewed X-inactivation?

A

80% of cells show preferential inactivation of one X-chromosome compared to the normal 50:50 expression

49
Q

What is the difference between gonadal and germline mosaicism?

A

Same concept, gonadal only in females, germline in both

50
Q

What is non-mendelian inheritance?

A

When a disease isn’t explained by a dominant, recessive or X-linked mode of inheritance

51
Q

Explain the risk in close family of multifactorial inheritance

A

Since a unique blend of environment and genetics leads to the disease, risk of condition is significantly higher in relatives than general population

52
Q

What is the population risk of schizophrenia?

A

1%

53
Q

What is liability?

A

A single entity considering genetic and environmental causation

54
Q

What is somatic mosaicism?

A

Certain tissues have a genetic variant whilst some don’t

55
Q

How are symptoms of mitochondrial disease caused?

A

Lack of energy to drive cellular functions as less ATP produced

56
Q

What is homoplasmy?

A

All mitochondria in cell have same genetic code

57
Q

What is hetroplasmy?

A

Certain proportion of mitochondria in a cell has a genetic variant

58
Q

What does a greater proportion of mutant mitochondria mean?

A

Increased likelihood of disease

59
Q

Are males and females equally affected by mitochondrial disease?

A

Not quite, both can be affected but only ova are large enough to contain significant numbers of mitochondria. Passed down maternally but if a male gets it from his mother he can’t pass it on

60
Q

What is Leber’s optic neuropathy?

A

Mutation in mitochondrial DNA which encodes complex 1 (mitochondrial enzyme for generating ATP) causing gradual onset of painless visual loss

61
Q

Who is more likely to be affected by Leber’s optic neuropathy?

A

Males, reason not known why

62
Q

What are imprinted genes?

A

One of the two autosomal genes from maternal or paternal side are switched off

63
Q

How can imprinted genes cause disease?

A

When imprinting is altered, and genes are switched on or off inappropriately

64
Q

Give an example of how imprinted genes can cause disease

A

If maternal imprinting occurs but the male gene undergoes a deletion mutation, no functioning gene is given leading to disease

65
Q

What is Prader-Willi syndrome?

A

Deletion of male (paternal) gene at chromosome 15p (short arm) leading to floppy baby with learning problems and obesity

66
Q

What is Angelman syndrome?

A

Deletion of female (maternal) gene at chromosome 15p (short arm) leading to average size baby, epilepsy and learning problems

67
Q

What are single nucleotide variants?

A

Change of one nucleotide (wild-type) to another nucleotide (mutant)

68
Q

What are 3 possible results of single nucleotide variants?

A

Synonymous - no alteration to protein
Non-synonymous - alteration to protein
Missense - 1 amino acid altered (no change to protein as degenerate nature of DNA)

69
Q

How can single nucleotide variant cause loss of function?

A

Frameshift affect, STOP codon formed, splice site variant

70
Q

What is nonsense-mediated decay?

A

Stop codon formed so mRNA isn’t properly processed and destroyed

71
Q

What types of change can insertion or deletion of nucleotides cause?

A

In-frame change - multiple of 3 nucleotides therefore loss or gain of a single amino acid
Out-of-frame change - premature STOP codon formed

72
Q

What are copy number variants?

A

Deletion or duplication of a segment of a chromosome

73
Q

What is the difference between trisomy and copy number variants?

A

Trisomy affects the whole chromosome, copy number variants only affect segments

74
Q

What is more harmful, deletion or duplication?

A

Deletion

75
Q

What is comparative genomic hybridisation?

A

Lab technique used to detect changes in the number of copies of DNA sections

76
Q

How is trisomy 21 detected?

A

In pregnant mothers blood as fetal DNA passed into bloodstream

IMMS (2 decks)

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