S13 Mutations Flashcards
What is Robertsonian translocation?
When p arms of acrocentric are lost and two q arms join together - to 2 sets of genetic info on one chromosome (p arms are so small, contain no/v little genetic info) - leads to 45 chromosomes rather than 46
Can a person still be healthy with robertsonian translocation?
Yes
What is aneuploidy?
Occurs due to non-disjunction of chromosomes (triosomy or monosomy)
Give an example of triosomy
Down’s syndrome
Give an example of monosomy.
Turner syndrome
What is mosaicism? When does it occur?
Cells have a variation of chromosomes that are normal, monosomy or triosomy.
Occurs if non-disjunction happens after the 1st zygotic division.
What are microscale mutations?
Deletion
Substitution
Addition
What are macroscale mutations?
Duplication Inversion Deletion Translocation Substitution
What is polyploidy? Give an example.
When a cell gains a haploid set of chromosomes so it becomes 3n (69 chromosomes rather than 46).
Polyspermy - when two sperm fuse with one egg cell.
Give examples of exogenous causes of mutations.
Ionising radiation
Free radicals
Mutagenic chemicals
Anti-cancer agents
Give examples of endogenous causes of mutations.
DNA replication defects
Transposable elements
What is a non-exogenous/non-endogenous cause of mutation?
Spontaneous events
What are spontaneous events that lead to mutations?
E.g. Spontaneous deamination - conversion of C to U - affects DNA replication - strands of same DNA will have different sequences
What are transposable elements?
DNA sequences that can change location (either into a gene, at the start of a gene or outside a gene)
May or may not have an affect on a gene
Affect could be not expressed or changes the start/stop codon
If a person is heterozygous, is the recessive allele still expressed?
Yes, it is justoverridden by the dominant allele expression
What is a SNP?
A single nucleotide polymorphism.
A change in a single nucleotide base to another base.
What are the two types of substitution?
- Transition - change to same base type
2. Transversion - change to different base type
What is a missense mutation?
A change in base that leads to a change in amino acid
What is a synonymous mutation?
A change in base that leads to no change in the amino acid
What is a nonsense mutation?
A mutation that results in a premature stop codon forming
What are 4 regulatory sequence mutations?
- Prevention of mRNA splicing
- Reduction in mRNA stability (linked to capping and polyadenylation)
- Alteration of promotor activity
- Alteration of translation initiation (change to AUG codon)
What molecular techniques can be used for cytogenic testing?
- FISH (fluorescence in situ hybridisation)
- Microarray hybridisation
- Karyotyping
- DNA sequencing
What is cytogenic testing?
Examining chromosomes to identify structural abnormalities
What are the advantages of cytogenic testing?
- Leads to accurate diagnosis and prognosis
- Allows for better clinical management
- Allows assessment of reproductive risks
- Allows for prenatal diagnosis
What do balanced and unbalanced mean in terms of mutations?
Balanced - no genetic info is lost/no phenotypic changes are apparent
Unbalanced - not balanced
Give 7 reasons for cytogenic testing referral.
- Prenatal diagnosis
- Birth defects
- Abnormal sexual development
- Infertility
- Recurrent fetal loss
- Leukaemias
- Solid tumours
What is the difference between an oncogene and proto-oncogene?
Oncogene - a gene that causes cancer
Proto-oncogene - a gene that, if mutated, cause cancer (becomes an oncogene)
What is a mutation?
A heritable alteration in a gene or chromosome and the process that produces the alteration
What type of mutation causes sickle cell anaemia?
A missense base substitution mutation that results in one amino acid change. Glu to Val
