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Y3 TRANSITION > Genetics > Flashcards

Genetics Flashcards

1
Q

What direction is the DNA chain read?

A

5 Carbon — 3 Hydroxyl (strands in antiparallel fashion)

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2
Q

What are the bases in DNA vs RNA

A

A-T, C-G

A-U, C-G

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3
Q

Describe the formation of a chromosome

A

Association of the DNA strand with histone proteins which wind together

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4
Q

Define G0 phase of the cell cycle

A

Most cells are resting, carrying out their normal function

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5
Q

Define G1 phase of the cell cycle

A

1st growth phase as chromosomes become ready to be replicated

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6
Q

Define S phase of the cell cycle

A

DNA replication occurs

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7
Q

Define G2 phase of the cell cycle

A

2nd growth phase involving proteins etc.

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8
Q

Define M phase of the cell cycle

A

Mitosis - mechanical separation of cell into two daughter cells
Two daughter cells are identical, diploid cells
PMAT: prophase, metaphase, anaphase, telophase

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9
Q

Variation occurs during meiosis by two main methods, which are?

A

Crossing over

Independent segregation of homologous chromosomes

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10
Q

In meiosis, one diploid cell becomes..

A

Four haploid daughter cells

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11
Q

Describe the process of transcription and translation from DNA into a protein

A

DNA is transcribed to pre mRNA
Pre mRNA is spliced to mRNA
mRNA is translated to protein
Protein is modified and modified around the cell

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12
Q

What is the difference between introns vs exons?

A

INTRONS: non coding sequences of mRNA not in final protein (spliced out)
EXONS: coding sequence of mRNA not in final protein (1-2% codes)

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13
Q

Give examples of sequence variations between genes and within genes respectivey

A

Single nucleotide polymorphisms (SNPs) Deletions/duplications

Changes in promotor or exon sequence
Copy number variations (CNVs) - extra or missing stretches of DNA

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14
Q

A polymorphism is…

A

A change in the genome that does not cause disease in its own right, but can predispose to a common disease (has a population frequency 1%)

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15
Q

Each copy of the genome is slightly different. True/False?

A

True
Everyone has new genetic variants that their parents don’t
New mutations are also acquired during meiosis

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16
Q

What percentage of the human genome is exons?

A

2-3% of 30 million bases

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17
Q

A chromosome consists of…

A

Telomeres at each end
Short arm (p)
Centromere
Long arm (q)

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18
Q

A chromosome is acrocentric if…

A

The p (short) arm is so short it is hard to observe

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19
Q

An aneuploidy is…

A

An abnormal number of chromosomes

Monosomy - missing chromosome from one pair Trisomy - extra chromosome in a pair

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20
Q

Reciprocal translocations are when…

A

Segments from two different chromosomes have been exchanged

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21
Q

Robertsonian translocations are when…

A

A chromosome attaches to another chromosome at the centromere
Only occurs with 13, 14, 15, 21, 22 - two acrocentric chromosomes stuck end-end creating a normal phenotype

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22
Q

Monosomy of the sex chromosomes causes…

A

Turners syndrome 45XO

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23
Q

Trisomy of chromosome 21 causes…

A

Downs syndrome

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24
Q

What is FISH?

A

DNA probes specifically bind to areas of individual chromosomes and apply a fluorescein stain to make the chromosome visible
Useful for detecting aneuploidies

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25
Q

What is Array CGH?

A

Genomewide search to detect polymorphisms (deletions or duplications) using dye and a scanner to show abnormalities between the sample and a reference

26
Q

Extra chromosome 18 causes…

A

Edwards syndrome

27
Q

Extra Y/X chromosome causes…

A

Klinefelters syndrome

28
Q

Give two methods of targeted testing for small genetic changes

A

PCR - original DNA strand is duplicated and then copies are made increasing the mutation which is detected when compared to the trace
NGS - DNA fragmented and rebuilt using the reference to show mutations

29
Q

Give types of point mutations

A

MISSENSE single nucleotide change creates a codon that codes for a different AA
NONSENSE single nucleotide change codes for a premature stop codon
INSERTION (in-frame or out-of-frame)
DELETION (in-frame or out-of-frame)

30
Q

Autosomal dominant disease occurs when…

A

There is one faulty copy of the gene

Seen in all generations 50% risk of affected child if parent affected

31
Q

Autosomal recessive disease occurs when…

A

There are 2 faulty copies of the gene
Often only one generation affected
25% risk of affected child if parents are carriers Increased likelihood if parents are related

32
Q

X-linked disease occurs when…

A

The disease is carried on the X-chromosome

  • only 50% of male children of a female carrier affected
  • 50% of female children of a female carrier affected
  • All male children of a male carrier normal
  • All female children of a male carrier will be carriers
33
Q

What is a caveat?

A

Female carrier shows mild features of X-linked disease

34
Q

Process preventing a double dose of gene products

A

X INACTIVATION: one X chromosome of females randomly inactivated using XIST gene of XQ13 via METHYLATION

35
Q

Methylation inhibits which process?

A

DNA transcription - chemic modification that does not change base sequence but interacts with histones on DNA

36
Q

The term used to describe X inactivation ‘gone wrong’ is….

A

SKEWING: Inactivation of one X chromosome favoured over another - mutation in XIST gene - results in uneven number of cells with X chromosome inactivation

37
Q

Penetrance is defined as…

A

The likelihood of having the disease given you have the genetic mutation

38
Q

Mendelian inheritance encompasses which disorders?

A

Autosomal dominant
Autosomal recessive
X-linked
Mitochondrial

39
Q

Penetrance in…

a) Mendelian disorder
b) Multifactorial disease

A

a) High - controlled by mutation in single gene with a small environmental input (usually rare disease)
b) Low - genetic change attributed to environmental input (usually relatively common disease)

40
Q

What is the common disease - common variant hypothesis?

A

Common disease causing variants will be found in all human populations which show a disease but not necessarily expressed in phenotype

41
Q

What is imprinting? What is it controlled by?

A

Variation in gene expression depending on which parent you inherit the gene from e.g. in Angelman’s syndrome, mother’s UBE3A works fine but father’s is methylated - controlled by methylation

42
Q

What is mosaicism?

A

Occurs when cells within the same person have a different genetic makeup (causes cancer)

43
Q

Cancer is most often inherited as a high penetrance Mendelian disorder. True/False?

A

False

More usually multifactorial

44
Q

Risk of breast cancer:

a) High
b) Medium
c) Low (population risk)

A

a) BRCA1 mutation
b) mother/sister breast cancer at 45
c) mother with breast cancer at 70

45
Q

Chromosome changes indicate treatment in cancer. What is the treatment for Her2 amplification?

A

Monoclonal antibody

Trastuzamab

46
Q

Chromosome changes indicate treatment in cancer. What is the treatment for Philadelphia chromosome?

A

Tyrosine kinase inhibitor

Imatinib

47
Q

Any genetic change you see may be…

A

A disease-causing mutation
A polymorphism
A variant of unknown significance

48
Q

How do you differentiate between a polymorphism and a disease causing mutation?

A

Is it de-novo? (?Is it present in the child but not both normal parents)
Is it in the right gene?
Has it been reported before? (? % of population)
What does it do to the protein? (?frameshift)

49
Q

What is the central dogma?

A

The two-step process, transcription and translation, by which the information in genes flows into proteins: DNA → RNA → protein`

50
Q

What is the most likely reason that a single base mutation has no effect on protein sequence?

A

Codon usage shows redundancy
Lots of combinations of bases and less amino acids, so different combinations can make the same amino acid - almost always 3rd base

51
Q

What is the reason for a person carrying a mutation but not showing features of a disease?

A

It has variable penetrance

52
Q

Why is NGS better than sanger sequencing?

A

It allows sequencing of a much larger number of genes

53
Q

Why is aCGH preferable to karyotyping?

A

It has higher resolution

54
Q

What characteristic of a cancer cell is central to allowing it to acquire further new characteristics?

A

Genomic instability

55
Q

Which ethical principle is most important in genetic counselling for your patient if they ask for a test?

A

Patient autonomy

56
Q

What is a synonymous mutation?

A

A change in the DNA sequence that codes for amino acids in a protein sequence, but does not change the encoded amino acid

57
Q

How do you calculate the pedigree risk of a child being affected?

A

Carrier risk of parent x population risk x risk of inheritance (AD or AR)

58
Q

Name the medication that works for carriers of the G551D mutation. How does it work?

A 
Ivecaftor
It affects ion channel opening (class 3)
59
Q

What is the difference between symptomatic and presymptomatic testing?

A

Symptomatic - clinical presentation

Presymptomatic - risk of inheritance

60
Q

How do you determine the genetic risk of a child inheriting CF?

A

Carrier risk e.g. of mother x
Population risk e.g. of husband x
Risk to fetus of inheriting mutation (AD or AR)

Y3 TRANSITION (10 decks)

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