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Principles > Genetics > Flashcards

Genetics Flashcards

1
Q

What direction is DNA read and replicated?

A

5’ to 3’

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2
Q

What are the parts of DNA that are used to code for proteins ?

A

Exons

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3
Q

What is the amount of protein produced determined by?

A
  • rate of transcription
  • rate of splicing to mRNA
  • half life of mRNA
  • rate of processing polypeptide
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4
Q

Why is every genome different?

A
  • changes in the promoter sequence
  • changes in the exon sequence (both ones that change an amino acid and those that don’t)
  • single nucleotide polymorphisms (SNPs)
  • larger deletions or duplications

-crossing over and independent assortment in meiosis

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5
Q

What are polymorphisms?

A

-any variation in the human genome that has a population frequency of greater than 1%
Or
- any variation in the human genome that does not cause a disease in its own right but may predispose a common disease

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6
Q

What does it mean that DNA replication is imperfect?

A

Every cell in your body has mutations acquired during mitosis which the parents don’t

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7
Q

How are chromosomes recognised?

A

-binding patterns with specific stains
-length
Position of centromere, telomeres
-length of short and long arms (short arm not as important)

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8
Q

What is a balanced chromosome?

A

A chromosome in which all the material is present

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9
Q

What is an unbalanced chromosomal rearrangement?

A

When there is extra or missing chromosomal material. Usually 1 or 3 copies of the same genome (developmentally bad)

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10
Q

What is a aneuploidy ?

A

A whole extra or missing chromosome

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11
Q

How would chromosomes causing Down syndrome be written in nomenclature ?

A

47XY + 21

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12
Q

What does one extra long chromosome 14 mean?

A

This can cause Down’s syndrome because a third chromosome 21 has translocations on to chromosome 14

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13
Q

What does trisomy 14 lead to?

A

Miscarriage

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14
Q

What happens to embryos with only one chromosome 21?

A

Miscarriage

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15
Q

What does trisomy 19 lead to?

A

Edwards syndrome (children will not survive)

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16
Q

What is robertsonian translocation?

A

When two acrocentric chromosomes are stuck end to end - leads to increased risk of trisomy in pregnancy

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17
Q

What are examples of X chromosome aneuploidy ?

A

45 X = Turner syndrome
47 XXX = triple X
47 XXY = Klinefelter syndrome

(X chromosome aneuploidy is better tolerated because of X inactivation)

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18
Q

What are reciprocal translocations?

A

One part of a chromosome swaps with another (doesn’t affect parent phenotype only offspring)

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19
Q

Roughly what percentage of translocations result in normal or balanced genomes?

A

50%

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20
Q

What can unbalanced translocations lead to?

A

Miscarriage and dysmorphic delayed children

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21
Q

What is aCGH?

A

The first line chromosome test , it is genomewide and also finds lots of polymorphisms.
Array CGH can detect any size of imbalanced but CANNOT detect balanced rearrangements
Analyses for deletions and duplications

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22
Q

Where do mutations come from?

A
  • one parents mutation germ line
  • new mutations in gametogenesis
  • one parent is mosaic (has two or more types of cells with different genetic constitution)
  • mutation occurs post-zygotes i.e the child is mosiac
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23
Q

What can chromosome changes do?

A
  • Activate an oncogene

- delete a tumour supressor

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24
Q

What does HER2 FISH do?

A

genetic test done on breast cancer tissue to see if cells have an extra copy of HER 2 gene

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25
Q

What is the Philadelphia chromosome?

A

When there has been translocation between chromosome 9 and 22

26
Q

What are the techniques for analysing DNA?

A
  • aCGH
  • PCR
  • NGS (next generation sequencing)
27
Q

What does PCR allow you to do?

A

To select one small piece of the genome and amplify it. Although it is only effective if you know what you are looking for.

28
Q

What does next generation sequencing (NGS) allow you to do?

A

-sequence the entire genome or known exons. (Relatively cheap)

29
Q

What do introns do?

A
  • regulate genes
  • space genes out (insulated genes from promoters)
  • provides substrate to expand genome
30
Q

Where can mutations act?

A

Promoters, when splicing, base changes coding for a stop, altering amino acid sequence.

31
Q

What is the wild type?

A

The “normal” code - the most common type

32
Q

What do the nomenclature c. and p. mean?

A 
C. = change in the mature mRNA sequence
P. = change in the peptide sequence
33
Q

What is the nomenclature for c. changes?

A

267 G>A substitution
267 DelG deletion
267 InsA insertion
267 +2T>A substitution in intron

34
Q

What is the nomenclature for P. changes?

A

Ile122val substitution
Ile122Ter / Ile122* premature stop
Ile122thrfs deletion causing frameshift

35
Q

How do you know the difference between a polymorphism and disease causing mutations?

A

By examining:

  • if it matches expected inheritance
  • if it’s in the right gene
  • if it’s been reported before
  • what it does to a protein
36
Q

What is penetrance?

A

The likelihood of having a disease if you have the gene mutation.
100% penetrance means you will always get the disease if you have the mutation.
Diseases caused by a single gene tend to have high penetrance

37
Q

What are example of Mendelian inheritance?

A

(Diseases caused by inherited genes > big genotype influence small environmental influence )

  • autosomal dominant
  • autosomal recessive
  • X-linked
  • mitochondrial
38
Q

What are examples of non Mendelian inheritance?

A

Methylation/ imprinting
Mitochondrial inheritance
Mosaicism
(MULTIFACTORIAL > lots of small genetic effects and a big environmental affect)

39
Q

If a mother passes on her X chromosome which is a carrier for a particular disease how will her children be affected?

A

Daughter will be a carrier and the son will be affected

40
Q

Why do female carries only show minor features of disease?

A

Due to X-inactivation hard of their chromosomes are normal and half aren’t.

41
Q

If an affected male (with x-linked disease) has children what will happen to them?

A

The females will be carriers and males will be normal

42
Q

What are SNPs?

A

single nucleotide polymorphisms
= alterations in a single base every 100 to 300 base pairs.
These do not cause diseases but can make you more prone to them. Most have no effect.

43
Q

What are CNVs?

A

Copy number variants are extra or missing stretches of DNA. They are highly prevalent in the genome.

44
Q

what is cancer in terms of genetics?

A

a disease of somatic mosaicism largely caused by post-zygotic mutations

45
Q

what does it mean that cancers are heterogeneous?

A

each cancer has different properties, cell lines and tissues as over 500 genes are implicated.

46
Q

what are driver and passenger mutations?

A 
driver = mutations driving carcinogenesis
passenger = incidental mutations that happen because the tumour is unstable.
47
Q

what is epigenetics?

A

the study of changes in gene expression without a change in DNA sequence - can involve DNA methylation or interaction with histone proteins.

48
Q

what is methylation?

A

adding methyl groups to the C5 position of cytosine bases just before guanine bases.

  • it prevents transcription by modifying histones
  • deamination can then occur (removal of NH3) to give a thymine
49
Q

what is the effect of hypermethylation?

A
  • can happen in tumour surpressors
  • tabacco carcinogens drives hypermethylation
  • start as a foetus
  • cancer causing
50
Q

what are the two types of driver mutations?

A

tumour suppressors and oncogenes

51
Q

what may cancer cells do to stop regulation of cell numbers?

A
  • produce their own extracellular growth factors
  • overexpress growth factor receptors
  • have constitutionally active proteins that do not require phosphorylation.
52
Q

how are oncogenes activated?

A
  • oncogenes are activated from proto-oncogenes due to dominant gain of function mutations
  • activated by point mutation, translocation or gene amplification.
53
Q

what do oncogenes do once activated?

A

produce excess amounts of protein and hyperactive protein.

54
Q

what does the BRAF oncogene do?

A

codes for a Raf kinase protein involved in signal transduction in the ,MAP-K pathway.
-point mutation in the BRAF gene removes the need for phosphorylation so the signal is always switched on.

55
Q

what is vemurafenib?

A

a specific tyrosine kinase inhibitor for V600E mutation.

- prevents tumour formation but can encounter resistance.

56
Q

what does trastuzumab do?

A

stop HER2 amplification by binding to receptors preventing them signalling for cellular proliferation.

57
Q

what does imatinib do?

A

binds to mutated BCR-ABL protein in Philadelphia chromosome to stop it functioning.

58
Q

what are tumour suppressors?

A

genes whose loss results in carcinogenesis.
normally they act as anti growth signals
tumour suppressor mutations are recessive.

59
Q

describe retinoblastoma

A

pRb is a tumour suppressor occurring at G1 checkpoint. a mutation in the Rb gene results in loss of function of RB and retinoblastoma.
it can be hereditary or sporadic.

60
Q

what is the two hit hypothesis?

A

says that somebody with 1 mutation in their tumour suppressor genes becomes a susceptible carrier (loss of heterozygosity) and somebody with two mutated tumour suppressor genes get cancer.

61
Q

what is oncogenic signature?

A

when cancer develop genomic instability and gain a high level of mutability they can evolve. this is driven by driver mutation and paired with loss of DNA repair is what allows cancer evolution.

62
Q

what features of cancer suggest inherited susceptibility?

A
  • several relatives
  • relatives with related cancers
  • unusually early age of onset
  • bilateral tumours in paired organs
  • tumours in two organ systems in one individual.

Principles (15 decks)

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