Flashcards in Mutations & Diagnostic Tools Deck (105)
What is a mutation?
A mutation is a heritable alteration in a gene or a chromosome, caused by a change in the sequence of amino acids
Name a major source of ionising radiation.
Describe what a transposable element is, and define some of their characteristics.
A transposable element is a specific DNA sequence (usually containing more than 1 gene) that move (as a discrete unit) to a random site - they're always contained within DNA and are never in a free form, and can insertion ally inactivate target genes
Are larger or smaller genes more susceptible to transposable elements?
Larger genes, as they have a greater area and usually are composed of a greater number of genes
What is the difference between a 'micro' and a 'macro' mutation?
A 'micro' mutation is a mutation of a single nucleotide base (insertion, deletion, substitution etc) while a 'macro' mutation is a mutation that describes changes on a chromosomal level
What is the difference between a transition and a transversion?
A transition is a nucleotide change to the same type of base (e.g. purine-purine or pyrimidine-pyrimidine), while a transversion is a nucleotide change to a different type of base (e.g. purine-pyrimidine or vice versa)
What mutation produces sickle cell anaemia?
A substitution mutation (missense) in the 6th amino acid on codon 7 from a glutamic acid to a valine
What is a mis-sense mutation?
A mutation that leads to a change in the amino acid in a polypeptide sequence
What is a silent/silence mutation?
A mutation that causes no change in the amino acid sequence coded for
What is a nonsense mutation?
A mutation that causes a (premature) stop codon
What is a frameshift?
A change in the nucleotide reading frame, by either a deletion (-1) or an addition (+1)
What is an inversion?
The rearrangement of a chromosome where a segment of it is reversed
Does an insertion of 3 nucleotides cause a frameshift?
No, as the frame will be read the same across the whole DNA sequence, only now there is a new codon inserted
What is the difference between a missense and a nonsense mutation?
- a nonsense mutation is a change in the nucleotide sequence where a stop codon is formed
- a missense mutation is a change in the nucleotide sequence where a different a amino acid is coded for
What is the difference between an oncogene and a proto-oncogene?
A proto-oncogene is a wild-type gene that regulates cell division, while an oncogene is a mutated form that is often unable to adequately regulate cell division (and as such is highly implicated in many cancers)
Why is a 'gain of function' mutation more likely to infer a dominant trait than a recessive trait?
If a 'gain of function' mutation was recessive there would be no gain in function as it would still be secondary to the dominant allele - a 'gain of function' mutation must therefore be dominant as to gain the function, the protein it codes for must still work, only in an enhanced way - if it wasn't enhanced, either the other allele would attribute to ensuring the old proteins function, or the cell wouldn't be viable and die (meaning there would be no gain of anything)
Are all mutations harmful?
No, as some may infer evolutionary advantages (the whole principle of evolution is based on genetic mutations)
How is nitrous acid formed? How does this cause genetic mutations?
It is formed from the nitrates and secondary amines formed in the stomach under acidic conditions -
What is cytogenetics?
The study of the genetic constitution of cells through the visualisation and analysis of chromosomes
Concerning leukaemia, why might cytogenetics be a useful diagnostic tool?
Various chromosomal translocations can infer the specific type of leukaemia an individual is suffering
What is aneuploidy? Give 4 specific examples.
Aneuploidy is an abnormal number of chromosomes, due to errors in cell division at meiosis:
- Down syndrome - a trisomy, an extra chromosome 21
- patau syndrome - a trisomy, an extra chromosome 13
- Edwards syndrome - a trisomy, an extra chromosome 18
- Turner syndrome - a monosomy, female missing an X chromosome
How would you write the Karyotype of a standard female in a chromosome report? What about a standard male?
How would you write the Karyotype of a male with Down syndrome in a chromosome report?
What is unique about Turner syndrome?
It is the only monosomy that is still viable
What is amniocentesis? When should it be carried out? Is there a risk of miscarriage?
Amniocentesis is a test a female can undergo during pregnancy to check whether the embryo has a genetic disorder - it involves removing and testing a small sample of cells from the amniotic fluid, which surrounds the foetus in the womb - this is carried out after around 15 weeks, and gives a 0.8% chance of a miscarriage
What is chorionic villus sampling? When should it be carried out? Is there a risk of miscarriage?
Chorionic villus sampling is a test a female may be offered during pregnancy to check if the embryo has a genetic order - this involves removing and testing a small sample of cells from the placenta - this is carried out around 11-12 weeks after gestation, and gives a 1.2% of miscarriage
What is polyploidy? How would you write this in a chromosomal report?
Polyploidy is the gain of a whole haploid set of chromosomes, producing triploidy
What is the most common cause of polyploidy?
Polyspermy - fertilisation of an egg by more than one sperm (usually 2 sperm)
What percentage of pregnancies result in triploidy? What about tetraploidy?
Triploidy occurs in around 2-3% of all pregnancies (most of these embryos are not viable) - tetraploidy occurs in 1-2% of all pregnancies