chromosomal abnormalities Flashcards
what is an ideogram
shows where you expect to see the bands on each chromosome after staining
non-disjunction
if it occurs in the first meiosis both pairs go to one cell so you get two copies in two cells
can also happen in second division so you end up with one gamete with two copies, one with none and two with one copy
what causes down syndrome
trisomy 21,3
what causes Edwards syndrome
trisomy 18
what causes Patau syndrome
trisomy 13
what causes Turner syndrome
having only one X chromosome
what is reciprocal translocation
can happen between long arm of chromosome 2 and chromosome 18-
balance exchange of material, can get unbalanced offspring which is likely to miscarry
what is Robertsonian translocation
two chromosomes known as acrocentric, centromere based at top of chromosomes, if join at centromere then forms a new chromosome and both lose short arm, affects segregation
unbalanced rearrangements- deletion
material is deleted
deletion 15q - prader willi/angelman syndrome
FISH
fluorescence in situ hybridisation
use DNA probes labelled with fluorophores, they are hybrid directly to the chromosome preparation or interphase nuclei
microarrays
new technology, improves the resolution for setection of cytogenetic abnormalities, as more patients are tested by microarrays we are contributing to a database of cytogenic and phenotypic abnormalities
role of cytogenetic in acquired abnormalities
confirmation of malignancy, classification of a disease type, prognosis, monitoring
non-random changes
close association with disease sub-type, association with clinical feature, association with lineage, no specific association, apparent multiple association
fusion/hybrid genes
breakpoints occur within the two genes involved. Fusion creates a hybrid gene which gives rise to chimaeric protein
deregulation
juxtaposition of gene to a regulating gene (eg igH). altered regulation can result in increased transcription and neoplastic growth
