NDJ Flashcards
what % of karyotypically abnormal foetuses are due to wrong number of chromosomes?
90
what is inheritence of the wrong number of chromosomes due to errors in?
meiotic chromosome segregation
when are NDJ events more likely?
when fewer crossovers between homologous chromosomes and more likley is crossover closer to telomere
what is the most common chromsomal abnormality that causes miscarriage?
polyploidy and of this triploidy
most common trisomy at point of conception?
trisomy 16
what is most common trisomy in live births?
downs, trisomy 21
most common aneuploidy overall
45X turners
why are sex aneuploids normally tolerated?
x chromsome can can be inactivated and Y contains few genes
what are the technologies used for a rapid preliminary report on cell free foetal DNA?
FISH and QPCR
what increases risk of mieotic NDJ?
age
what happens in mitotic NDJ?
gametes fuse normally, but during early embryo development chromosome NDJ occurs during mitosis
where are meosis errors more common?
in MI and in maternal gametes
what measures length of chromosome and amount of crossovers?
centimorgans
what does 1cM equal?
1% chance that 2 marks are separated due to a crossover
in meisosis I NDJ what were the chromosomes compared to standard ones?
shorter with fewer crossovers
in meiosis II NDJ what were the chromosomes?
longer with too many crossovers
what does cohesin consist of?
smc1 and 3 hetrodimer. in mitosis scc1 closes the loop, in meiosis its rec8
which bit of the chromosome in the cohesion the strongest?
the bit between the crossover and the telomere
what is faithful disjunction dependent upon?
distal sister chromatin cohesion, relative to the centromere
where are occytes arrested in foetal development?
prophase of meiosis I
why are maternal NDJ more common?
the long phase of meiotic arrest may mean that the cohesion complexes are damaged slightly. if there are only a few crossovers, may all get damaged and NDJ more likley
what is mocasism?
two or more cell populations with different genotypes within a single individual
what can cause mosoacism?
mitotic NDJ resulting in trisomic and monosomic daughter cells
what can confirm whether something is confined to the placenta?
amniotic fluid sample
how can normal cells form from a MI NDJ event?
trisomic rescue
what does maternal UPD of chromosome 16 cause?
growth restriction as a result of imprinted genes on chromosome
what does the confinement of a trisomic cell line to the placenta depend upon?
when the rescue event occured in development
what mechanisms can trisomic rescue occur by?
non-disjunction or anaphase lag
