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Principles of Disease > Genetics and Genetic Disorders > Flashcards

Genetics and Genetic Disorders Flashcards

1
Q

What process produces diploid cells from diploid cells?

A

Mitosis

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2
Q

What process produces haploid cells from diploid cells?

A

Meiosis

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3
Q

What processes produce diploid cells from haploid cells?

A

Fertilisation

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4
Q

What offspring receive an X chromosome from their father?

A

Daughters only

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5
Q

Describe a nucleotide monomer.

A

Deoxy or ribose sugar + base + phosphate

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6
Q

What charge is the phosphate group?

A

Negative

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7
Q

How many carbons exist in the sugar rings?

A

4 carbons (5th is side chain)

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8
Q

What direction is the chain of nucleotide monomers?

A

5’ to 3’

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9
Q

How are complimentary base pairs bound?

A

Via Hydrogen bonds.

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10
Q

Name the purine bases.

A

Adenine and Guanine

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11
Q

Name the pyrimidine bases.

A

Cytosine, Thymine and Uracil

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12
Q

How many hydrogen bonds are formed between Cytosine and Guanine?

A

3

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13
Q

How many hydrogen bonds are formed between Adenine and Thymine?

A

2

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14
Q

How many DNA bases exist?

A

5

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15
Q

What replaces thymine in RNA?

A

Uracil

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16
Q

What linkage forms covalent backbone if DNA?

A

Phosphodiester linkage

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17
Q

In what direction does the sense/leading strand of DNA run?

A

5’ to 3’

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18
Q

In what direction does the anti-sense/lagging strand run?

A

3’ to 5’

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19
Q

How is DNA described?

A

Semi-conservative and bi-directional

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20
Q

During replication, what enzyme ‘unzips’ the DNA?

A

Helicases

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21
Q

What enzyme controls elongation during DNA replication?

A

DNA Polymerases

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22
Q

In what direction does DNA polymerase work?

A

5’ to 3’

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23
Q

In lagging strand, what enzyme seals Okazaki fragments?

A

DNA ligase

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24
Q

What enzyme proof reads new double helix?

A

Nucleases

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25
Q

How is a base sequence of DNA transcribed into a base sequence in RNA.

A
  1. Initiation
  2. Elongation
  3. Termination
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26
Q

Where does transcription occur?

A

In nucleus

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27
Q

What regions of DNA are known as coding regions?

A

Exons

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28
Q

What regions of DNA are known as non-coding regions?

A

Introns

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29
Q

What determines the reading frame?

A

Initiation codon

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30
Q

Describe the post-transcriptional processing of RNA.

A

Exon splicing

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31
Q

What is required for the translation of mRNA?

A
  • rRNA for assembly plant
  • tRNA for translation of mRNA to AA sequence
  • AUG start codon
  • ribosome
  • stop codons (to disassemble ribosome and release polypeptide.
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32
Q

Where does translation occur?

A

In the cytoplasm

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33
Q

What does DNA package with histones form?

A

Chromatin

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34
Q

What are nucleosomes?

A

DNA wrapped around core of histone protein. ‘Beads on a string’.

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35
Q

What is chromatin?

A

Packed nucleosomes (supercoiled).

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36
Q

Further wrapping of chromatin fibre loops and nucleosomes form what?

A

Chromosome

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37
Q

What charge is histone proteins?

A

Positive (neutralises negatively charged DNA)

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38
Q

What is used in the laboratory to diagnose a genetic disease?

A

Karyotype

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39
Q

What is FISH?

A

Fluorescent In-Situ Hybridisation (visualise and map genetic material)

40
Q

In FISH, what probes can be used?

A
  1. Centromeric probes (determine chromosome structure)

2. Whole chromosome probes (detect translocations and rearrangements)

41
Q

Describe the types of structural chromosomal abnormalities.

A

Balanced or un-balanced rearrangements:

  1. Translocations
    a) Reciprocal (breaks in two chromosomes)
    b) Robertsonian (fusion of two acrocentric chromosomes)
  2. Deletions
  3. Insertions
  4. Inversions (paracecntric or pericentric)
42
Q

Give an example of a Robertsonian Translocation.

A

Down syndrome

43
Q

What is the first law of mendelian inheritance?

A

Law of segregation (during gamete formation, each member of the allele pair separates)

44
Q

What is the second law of mendelian inheritance.

A

Law of independent assortment (genes for different traits assort independently of another in the formation of gametes)

45
Q

Describe the characteristics of autosomal dominant traits.

A
  • each child has 50% chance of inheriting mutation
  • no skipped generations
  • equally transmitted by men and women
  • male to male transmission can occur
46
Q

Describe the characteristics of autosomal recessive traits.

A
  • unaffected parents have affected children
  • males and females equally affected
  • horizontal inheritance pattern
  • conditions usually have early onset
  • reduced penetrance than autosomal dominant
47
Q

What trait can be more common in ethnic groups?

A

Autosomal recessive trait.

48
Q

What is the risk for a sibling of an unaffected individual to be affected?

A

25% (1 in 4)

49
Q

Describe x-linked traits.

A
  • Males more commonly affected
  • If mother not carrier then affected males have unaffected children
  • All daughters are carriers from affected carriers and no sons inherit conditions.
50
Q

Describe the types of chromosomal mutations.

A
  1. Numerical
  2. Structural
  3. Mutations
51
Q

Give examples of numerical chromosome mutations.

A 
Down syndrome = trisomy 21
Patau's syndrome = trisomy 13
Edward's syndrome = trisomy 18
Kleinfelter's = 47XXY 
Turner's = 45X
52
Q

Give examples of structural mutations.

A

Translocations (reciprocal and robertsonian)
Deletions
Insertions
Inversions (paracecntric and precentric)

53
Q

Give examples coding mutations.

A
  1. Silent (ARG to ARG)
  2. Misense (ARG to GLY)
  3. Nonsense (ARG to STOP)
  4. Frameshift (deletion/insertion)
54
Q

What are the main types of chromosomal mutations?

A
  1. Non-coding
  2. Coding
  3. Point (transitions and transversions)
55
Q

Give 5 examples of molecular genetic technology.

A
  1. PCR
  2. Gel electrophoresis
  3. Amplification refractory mutation system (ARMS)
  4. RFLP
  5. DNA Sequencing
56
Q

What is the role of PCR?

A

Amplify single or a few copies of a segment of DNA

57
Q

What is required for PCR?

A

Sequence info, oligonucleotideprimers, DNA nucleotides and DNA polymerases.

58
Q

What is the role of gel electrophoresis?

A

Separates DNA fragments by size by applying an electrical current through an agarose gel matrix.

59
Q

What are the advantages of gel electrophoresis?

A

Speed, ease of use, sensitive, robust.

60
Q

Give an example of when RFLP is used?

A

Test for sickle cell anaemia. Uses restriction endonucleases to cut out genes.

61
Q

Give an example of a gold standard DNA sequencing method.

A

Sanger sequencing

62
Q

What is DNA sequencing used for?

A

Detecting mutations

63
Q

Define population genetics.

A

The frequency of alleles in whole population affects health of population.

64
Q

What is often associated with genetic variation?

A

Selective pressure changes.

65
Q

According to the Herdy-Weinberg equilibrium, genotype and allele frequencies remain constant. Is this true or false?

A

True

66
Q

What does non-random mating lead to?

A

Increase mutant alleles thereby increasing proportion of affected homozygotes.

67
Q

Describe two types of non-random mating.

A
  1. Assortive mating (choosing partners due to shared characteristics e.g deafness)
  2. Consanguinity (marriage between close blood relatives)
68
Q

Describe the effects of negative natural selection.

A
  1. Decrease reproductive fitness

2. Decrease prevalence of traits

69
Q

Describe the effects of positive natural selection.

A
  1. Increase reproductive fitness

2. Increase prevalence of adaptive traits.

70
Q

Define genetic drift.

A

Random fluctuation of one allele transmitted to high proportion of offspring by chance.

71
Q

Define founder effect/bottleneck effect.

A

Reduction in genetic variation that results when a small subset of a large population is used to establish a new colony.

72
Q

Cultural and geographic founder mutations can be subdivided into what?

A

Dominant (e.g BRCA1/2) & recessive (e.g CF)

73
Q

What are the basic mechanisms of inherited predisposition to cancer?

A
  1. Oncogenes (accelerate cell division)
  2. Tumour suppressor genes (inhibit cell cycle or promote apoptosis)
    “two-hit hypothesis”
74
Q

What is the result of failure of mismatch repair genes?

A
  • micro satellite instability (MSI).
  • cells with abnormally function MMR genes accumulate errors.
  • inherited cancer likely at young age.
75
Q

Describe most cancer susceptibility genes.

A

Dominant with incomplete penetrance. Need second mutation to develop cancer.

76
Q

Give two examples of predictive gene tests in cancer.

A
  1. BRCA 1/2 associations with breast cancer and lifetime risk
  2. Colorectal cancer (non-polyposis or polyposis)
77
Q

In the genetics clinic, what is the most important tool to investigate indirect linkages?

A

Drawing a pedigree.

78
Q

What needs to be considered when looking at genetics?

A

‘Founder effect’

79
Q

What is the steps in the clinical assessment in a genetics clinic?

A 
History
Pedigree
Clinical examination (individual and family)
Genetic test
Synthesis
80
Q

Who provides genetic counselling?

A

Clinical geneticist, counsellor, hospital doctor, GP, nurse

81
Q

What has caused wet lab costs to fall less that 50% and decreased the time taken to interpret data?

A

Next generation sequencing

82
Q

Describe two ethical issues related to genetic testing.

A
  1. Limitations - i.e some tests may not provide all the info families want and may require difficult decisions.
  2. Should info be obtained if no treatment or intervention exists?
83
Q

Describe non-mendelian inheritance.

A

Doesn’t fit in with Medel’s laws of segregation and independent assortment e.g gene conversion or intermediate phenotype.

84
Q

What are the mechanisms of complex inheritance?

A
  • Incomplete penetrance
  • Genomic imprinting
  • Extracellular inheritance
  • Anticipation
85
Q

Define penetrance.

A

Frequency at which a trait is manifested by individuals carrying the gene.

86
Q

Define epigenetic modifications.

A

Changes in gene function not explained by changes in DNA sequences.

87
Q

Define uniparental disomy.

A

Inheritance of a chromosome pair from one parental origin.

88
Q

Describe mitochondrial inheritance and give examples of mitochondria disease.

A

Mitochondrial disease affect tissues with high metabolic demand e.g Leigh’s syndrome, Leiber’s hereditary optic neuropathy, DM and deafness.

89
Q

What is recombination?

A

The process of forming new allelic combination in offspring by exchanges between genetic materials (as exchange of DNA sequences between DNA molecules). This process is a natural process, such as the crossing over between homologous chromosomes during meiosis.

90
Q

Does meiosis involve recombination?

A

Yes.

91
Q

Does fertilisation cause recombination?

A

Yes

92
Q

Describe FAP (familial adenomatous pulpous)

A

A hereditary colorectal cancer syndrome with severe colonic polyposis. Untreated polyposis leads to 100% risk of cancer.

93
Q

What are the assumptions underlying the Hardy-Weinberg equilibrium?

A
  • mating is random
  • population size is large
  • migration is negligible
  • All of this helps explain the difference between expected population (as per HWE) and observed population (what is actually seen in real life)
94
Q

What is the phenotype of a person with Kleinfelter’s (XXY)?

A

Male. The presence of a single Y chromosome, regardless of the number of X chromosomes, is what causes development as a male.

95
Q

Does mRNA have a distinct lifetime within the cytoplasm of the cell and its degradation helps control protein production?

A

Yes.

96
Q

What is the chance of and unaffected child whose parents are both carriers of cystic fibrosis to be homozygous for the normal allele?

A

In a family like this, each child has a ¼ chance of being affected (homozygous for the CF allele), a ½ chance of being a carrier (heterozygous and unaffected), and a ¼ chance of being homozygous for the normal allele and unaffected. So, of the unaffected children, 1/3 of them are homozygous normal.

Principles of Disease (9 decks)

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