L15 Chromosome abnormalities & cytoplasmic inheritance Flashcards
what is aneuploidy
abnormal number of chromosomes
what are the 3 types of aneuploidy and their characteristics
monosomy - loss of single chromosome (2n-1)
trisomy - an extra chromosome (2n+1)
tetrasomy - an extra pair of chromosomes (2n+2)
whats the normal human karyotype
males - 46, XY
femlaes 46, XX
what is non-disjunction
mistakes during meiosis that give aneuploid gametes
what happens in non-disjuction in meiosis 1
both pairs of chromosomes go to one side, and none of this chromosome go to the other daughter cell
forms 2 gametes w/ extra chromosome and 2 w/ missing chromosome
see onenote
what happens in non-disjunction in meiosis 2
1 division is normal
but in seperation of sister chromatid, one doesnt seperate
forms a daughter cell w/ an extra
a daughter cell w/ a missing
and 2 normal
see onenote
what % of human conceptions are aneuploid and how many of these are live births
20-50% aneuploidy
less than 0.5% make it to birth
which autosomal aneuploidy is inviable
all monosomies
(2n-1) are inviable
what is trisomy 21
down syndrome
what is trisomy 13 and 18
Patau syndrome & Edwards syndrome
(die few months after birth)
the numbers 13 and 18 relate to the chromosome that they affect
what’s the name of the test offered to women at 11-14 weeks
combined test
what’s the name of the test offered to women at 14-20 weeks
quadruple test
what do these tests do
assesses the RISK of developing aneuploidy, and if its higher than 1 in 150 then theyre offered a diagnostic test
what are the 2 methods to get cells from the fetus
chorionic villus sampling (CVS)
or
amniocentesis
after these cells are extracted, what can they do
culture the cells and and can determine the karyotype from this
what has recently been developed to improve this process
non-invasive prenatal testing (NIPT)
looks at foetal dna in mums blood
what is robertsonian translocation
another cause of down syndrome
chrom 21 and chrom 14
CARRIER - have normal chrom 14 and 21
translocation occurs, but carrier remains unaffected cuz they still have the same number of chromosomes
but they can pass down too many copies of chrom 21
causing downs in the offsprins
icl i dont rly get this but onenote ig
just know the name of it as another cause of downs
it is what it is
what is genetic mosaiscism
mix of normal cells and trisomy 21 cells
- comes from when embryo w/ trisomy 21
but then during early divisions
it loses the extra chromosome via non-disjunction
so depending on when and where this occurs, some individuals have many cells w/ trisomy and other have less
aneuploidy in sex chromosomes - the condition caused by monosomy in women
Tuner sydrome
or
XO
so one X is missing
sterile, short stature, learning difficulties
aneuploidy in sex chromosomes - XXY result
47,XXY
sterile males, feminised physique, majority not diagnosed
aneuploidy in sex chromosomes - what is Triplo-X
kinda obvs
47, XXX
female w/ extra X
mostly normal, may have some effect on fertility and intelligence
so most undiagnosed
aneuploidy in sex chromosomes - what is characteristics of XYY syndrome
fertile males
above avg height
majority not diagnosed
how does the mums age affect the risk of trisomy
the older the highe the risk of the child having trisomy
this is largely responsible as to why older women have higher rist of miscarriage
why are older women more at risk of trisomy
mostly due to non-disjunction at meiosis 1
but happens more because of loss of cohesion over time
since egg is formed before birth, cohesin (like glue between chromosomes) wears down
see onenote for more detail and diagram
so its more likely to form
what 2 places other than nucleus can dna be found in cell
mitochondira
chloroplast
what are the prokayotic features of these extranuclear genomes
they have circular DNA
and ribosomes of mitochondria and chloroplast are diff to the others in cytoplasm
and are sensitive to bacterial antibiotics
what do these prokaryotic features suggest about these structures
the endosymbiont theory
host cell = archaebacteria
a bacterial cell engulfed by host cell, and then this became the mitochondria
and then a second event of a photosynthetic prokaryote being engulfed, becoming the chloroplast
see onenote
what genes does mtDNA have in it
mainly components for translation (e.g. tRNAs and rRNAs)
and
structural genes for proteins involved in oxidative phosphorylation (so like all the enzymes and stuff)
how do we know that genes have transferred from mtDNA to the nuclear genome
the mtDNA is much smaller than what it would’ve originally been in the bacteria
what genes does cpDNA have in it
similar to mtDNA
codes for proteins involved in translation
and
structural genes involved in photosynthesis
what’s diff about the inheritance of mt and cp
they are only passed down from the mother and not the father
what contributes to maternal inheritance of the mt genome
eggs are larger than sperm
so egg would have >100,000 copies of mtDNA
sperm
and
egg has mechanism for destroying mtDNA in the sperm, so it’s destroyed after fertilisation
what does a pedigree look like for mt disease
females transmit the trait tom all their children
males never transmit the trait
how does mtDNA disease present in families
highly variable even within one family
same mutation amy cause diff signs and symptoms
whats the reason for the high level of variation in mtDNA disease
heteroplasmy
individual is carrying diff forms of mt with diff mtDNA
so a mosaic of normal and mutated mtDNA
so during segregation of mt in cell division, diff proportions of mutant mt are passed down
see onenote
mt replacement therapy (or three person baby)
maternal spindle transfer:
egg from mum w/ abnormal mt
donor egg w/o mtDNA disase
mothers nucleus (chromosomes and spindle) removed
donor egg denucleated
mums egg put inside donor egg and fertilised
whats the concerns that have come from this procedure
sometimes the mothers diseased mt also get transferred to the donor egg
