Topic 14 Flashcards
Define mutation and mutagenesis
mutation- a change in nucleotide sequence in DNA
mutagenesis- the process of mutation generation
What are transposable elements?
specific repetitive DNA sequences that move
‘jumping genes’ or transposons
ubiquitous (found in all lifeforms)
discrete units that transpose randomly
supernumerary
can make up a very large percentage of a genome
cause mutations
What is SNP?
single nucleotide polymorphism
anonymous SNP- no known effect
non coding SNP- outside a gene
coding SNP- inside a gene
What is transition and transversion?
transition- change to the same type of base
eg purine to purine
transversion- change to a different type of base
eg purine to pyrimidine
What are the four types of single nucleotide changes and the name of mutation?
change in the gene product (polypeptide or RNA)
- missense mutation, change in amino acid (or non- synonymous)
change the amount of gene product
- mutations affecting regulatory sequences
change the polypeptide length
- frameshift/ mutation of the stop codon/ nonsense (if creates a stop codon)
do not have an effect
- silent or neutral/ synonymous
What is polyploidy?
gain of haploid set of chromosomes
eg triploidy 3n= 69 chromosomes
most common cause is polyspermy (two sperm fertilise one egg)
occurs in 2-3% of pregnancies
What is aneuploidy?
loss or gain of whole chromosomes
trisomies and monosomies
caused by meiotic nondisjunction and in mitotic nondisjunction
What is mosaicism?
presence of two or more cell line in an individual
throughout the body or tissue specific
caused by mitotic nondisjunction
What are the types of structural abnormalities?
deletions
duplications
inversions (paracentric or pericentric)
substitutions or insertions
translocations
isochromosomes (double p arm or double q arm)
ring chromosomes (chromosomes fuse and form a ring)
marker chromosomes (extra bit of DNA on top of 46)
What is reciprocal translation and what are the meiotic consequences?
can be balanced or unbalanced
involves two chromosomes swapping segments
quadrivalent will form (rather than two bivalents)
segregation will have 3 possible ways (alternate, homologous, non- homologous centromeres) with 6 possible outcomes
3 to 1 nondisjunction
What is Robertsonian translocation and what are the meiotic consequences?
where two acrocentric chromosomes fuse (very small p arms fusing)
chromosome count of 45 in balanced carriers, robertsonian chromosome “acts” as one chromosome
females higher risk than males
trivalent will form
segregation with 6 possible outcomes
aneuploidy risk
What is cytogenetic testing?
cytogenetic analysis (eg karyotyping) FISH microarray hybridisation DNA sequencing plus more
Why do cytogenetic testing?
accurate diagnosis and prognosis of clinical problems
better clinical management
assess future reproductive risks
prenatal diagnosis
What are balanced and unbalanced abnormalities?
b- no genetic information lost and/ or no phenotypic changes present
ub- not balanced
need to consider the somatic or germ line consequences
