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Sem 1 - MCBG > 13 - Mutations > Flashcards

13 - Mutations Flashcards

1
Q

What is a mutation and what is mutagenesis?

A

Mutation - A change in the nucleotide sequence

Mutagenesis - Process of mutation generation

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2
Q

What is deanimation mutation?

A

Removal of an amino group from a molecule causing a change in base

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3
Q

What are some DNA level mutations and how do they occur?

A

- Exogenous sources (radiation, free radicals etc)

- Endogenous sources (transposable elements, replication defects)

- Spontaneously

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4
Q

Why does spontaneous deanimation always result in a mutation?

A
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5
Q

What are transposons?

A
  • Sit within chromosome
  • Greater length than one gene
  • Can move as discrete unit and insert themselves into another location (transposition)
  • Issue if inserted into genes as can cause non-functional polypeptide, inactive/activate gene

- Bigger the gene bigger the risk of transposition, e.g DMD

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6
Q

What is a SNiP?

A

Single nucleotide polymorphism

  • Where one nucleotide is different to the rest of the population
  • Anonymous SNP, coding SNP, non-coding SNP (not in gene)
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7
Q

What are micro mutations?

A
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8
Q

What are the two types of substitution?

A

Transition - Same base for same base

Transversion - Change to different base (pyramidine to purine)

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9
Q

What can a single nucleotide change result in?

A
  • No effect
  • Change polypeptide length
  • Change amount of product
  • Change gene product
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10
Q

What is the genetics behind sickle cell anaemia?

A
  • Autosomal recessive
  • Base substitution in codon 7 of HBB, changing 6th AA
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11
Q

What is a non-sense mutation?

A

Mutation causes a change in the stop codon so it is not recognised so polypeptide longer than should be

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12
Q

What is a missense mutation?

A

Mutation that results in a different amino acid being coded for

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13
Q

What is a synonymous mutation?

A

Substitution, same amino acid coded for. (could be due to wobble)

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14
Q

What is a frameshift mutation?

A

When there is a change in the number of nucleotides, not in the multiple of 3, so all the amino acids downstream are different

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15
Q

Why might a deletion of three bases not cause any affect, and why may it cause a drastic effect?

A
  • No frameshift so only one amino acid missing
  • If amino acid usually located in active site will cause non-functional protein but if not, not much difference to overall structure of protein
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16
Q

What is haemoglobin wayne and haemoglobin CS?

A
  • Normal alpha Hb: 141 aa
  • alpha wayne: 147 aa (deletion of A at 139 causing frameshift so stop codon not read)
  • alpha cs: 172aa (substitution in 142 stop codon so not read)

NON-SENSE MUTATIONS

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17
Q

How could a mutation lead to a change in the amount of a gene product?

A
  • Mutation in regulatory sequence
  • Alter promoter activity
  • Prevent mRNA splicing (splicing sites change)
  • Reduce mRNA stability (mutations in tails and caps)
  • Earlier start codon
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18
Q

What are haemoglobin lyon and leiden?

A
  • Leiden: Loss of Glu at 6
  • Lyon: Loss of Lys and Val at 17/18
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19
Q

What are the types of chromosome mutation?

A
  • Translocation (reciprocal/robertsonian)
  • Inversion (para/pericentric)
  • Duplication
  • Substitution
  • Deletion
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20
Q

What are the two types of chromosome inversion?

A

Paracentric: on one side of the centromere, within one arm

Pericentric: inversion occurs over the centromere

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21
Q

What happens during chromosome substitution (insertion)?

A

One part of a chromosome is moved from one chromosome to another

22
Q

What are the two types of protein translocation?

A

Reciprocal: Swapping of genetic material

Robertsonian: Breaking at the centromere on two acrocentric chromosomes. Lose the p arms, two q-arms fuse. Individual has 45 chromosomes

23
Q

Apart from the main chromosome mutations, what are three other structural mutations that can occur?

A

- Ring chromosomes (end break and fuse to ring)

- Isochromosomes (two p together, abnormal centromere split)

- Marker chromosomes (small fragements of chromosomes)

24
Q

What is polyploidy?

A

- more than two sets of homologous chromosomes (3n=69)

  • usually due to polyspermy
  • triploidy occurs in 2-3% of pregnancies and causes 15% of miscarriages
25
Q

What is aneuploidy?

A
  • Abnormal number of chromosomes
  • Due to non-disjunction in meiosis

- Not always lethal like polyploidy

- Doesn’t involve more than two sets of homologous chromosomes

26
Q

What are some examples of monosomy and trisomy?

A

Mono:

_-_Turners Syndrome 45,X

Tri:

- Down Syndrome 47,+21

  • Patau 47,+13
  • Edwards 47,+18
  • Klinefelter Syndrome 47,XXY
27
Q

Does chromosome non-disjunction only occur in some chromosomes?

A

No, all of them. Only some are visible as they are the only ones viable for life, rest can’t live

28
Q

What is Turner’s syndrome?

A
  • Lack of X chromosome
  • Only affects female
  • Only known monosomy
29
Q

What is Patau syndrome?

A
  • Trisomy 13
  • Mostly miscarry/still birth. 90% die in first year
30
Q

What is Edward’s syndrome?

A
  • Trisomy 18
  • Life span: 5-15 days
  • Maternal meiosis II error
31
Q

What is Klinefelter syndrome?

A
  • Trisomy XXY
  • Male with two X’s
  • Infertile
32
Q

What is Down syndrome?

A
  • Trisomy 21
  • Early alzheimers, hypotonia, heart defects, facial features distinct, increased risk of leukemia

- Critical region: 21q22 (don’t have to have full chromosome duplication to have downs)

33
Q

What is mosaicism?

A
  • When chromosome non-disjunction occurs in mitosis. Results in two or more cell lines
  • Occurs after first mitotic division and can save trisomy, reducing the number of cells in the body with trisomy
34
Q

What are balanced and unbalance chromosomal abnormalities?

A

Balanced - No genetic information is lost or gained and the phenotype is normal

Unbalanced - Abnormal chromosome has led to abnormal phenotype

35
Q

What is balanced translocation?

A

Reciprocal Translocation

- 2 chromosomes clean broken and material is swapped.

  • Leads to issues in meiosis as quadrivalents are formed
  • During meiosis balanced and unbalanced gametes can be produced depending on segregation
36
Q

When can reciprocal translocation be an issue?

A
  • Philadelphia Chromosome
  • Fusion of BCR-ABL gene on chromosome 22, kinase signally gene constantly on so cell uncontrollably divides
  • Associated with leukemia
37
Q

What is the issue with balanced translocation?

A
  • In meiosis a quadrivalent is formed rather than bivalent so different types of segregation
  • 3:1 non-disjunction
  • Alternate segregation
  • (Non-homologous) Adjacent 1 segregation
  • (Homologous) Adjacent 2 segregation
38
Q

What are the consequences of different types of segregation when meiosis occurs with chromosomes that have undergone translocation?

A
39
Q

If a couple with one being a carrier for reciprocal translocation, how would you work out the risk that they would have a child with an imbalance?

A
  • Analyse couples genes to see which chromosomes have been affected by translocation
  • Look up if anyone else has had the same translocation before and quote the risks
  • Work out based on the knowledge known
40
Q

What happens during meiosis with a person with a Robertsonian translocation and what happens to their offspring?

A
  • Person has 45 chromosomes
  • Trivalent formed at meiosis
  • Leads to risk of aneuploidy
  • Females with 45 at higher risk than males (oogenesis pauses in meiosis and trivalent very unstable)
41
Q

Why can people appear phenotypically normal but be infertile or have abnormal children?

A
  • They have balanced translocation which is not picked up on microarray
  • Could have two 21’s fused so end up with trisomy and downs
  • Infertile as odd number of chromosomes
42
Q

What is cytogenetics and why is it carried out?

A

Study of the genetic make up of cells through visualisation and analysis of chromosomes

- Better clinical management (e.g hormones for XXY)

- Pre-natal diagnosis

- Accurate diagnosis (identify syndrome, account for pregnancy loss)

- Assess future reproductive risks (affected baby or risk of unalive birth)

43
Q

How can cytogenetics be carried out?

A
  • Karyotyping
  • FISH
  • Microarray hybridisation
  • DNA sequencing
44
Q

What are some referral reasons for cytogenetic testing?

A
  • Delayed sexual development
  • Pregnancy loss
  • Prenatal diagnosis
  • Birth defects
  • Infertility
  • Leukemia
  • Tumours
  • Prognostic info for specific translocations
45
Q

What is a protooncogene and an oncogene?

A

Protooncogene - Gene that has the potential to become an oncogene if there are mutations

Oncogene - Gene that has the potential to cause cancer

46
Q

Can a mutation in bases very upstream cause a change in the gene product?

A

Yes! Could affect a regulatory sequence that normally stimulates an effector to start transcription, therefore more or less gene expression

47
Q

What is a gain of function mutation?

A

A mutation that leads to a new or enhanced function of a protein. Almost always dominant

48
Q

What is nitrous acid and how is it formed?

A
  • Sodium nitrate is a food additive in smoked meats
  • When gets into stomach it reacts with HCl to form nitrous acid
  • Nitrous acid is a mutagen which causes deanimation of C –> U
49
Q

What is the relationship between sickle-cell trait and malaria?

A
  • If you have sickle cell trait normally immune to malaria
  • Malaria is caused by a parasite that normally replicates within red blood cells
  • If red blood cells lysing then parasite killed before it can get to replicate
50
Q

Can you test for Down Syndrome whilst a mother is pregnant?

A

Yes NIPT. Can take a blood test from the mother at 9-10 weeks as their blood will contain some fetal DNA, not all the fetal chromosomes but some

Sem 1 - MCBG (20 decks)

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