Lecture 8 - Aneulploidy And Non-disjunction Flashcards
How could meiosis go wrong - what would happen is chromosomes didn’t recombine?
They would not be attached and therefore behave independently of one another. This means there would be 50% chance of them going to the same pole
How could meiosis go wrong - what would happen is crossing over happened to close to the telomere?
There’s not as much cohesin and therefore easier to lose which would cause sliding
What would happen is cohesin isn’t protected at the centromeres?
Sister chromatids separate and can go to either pole. If they go to the same one this is bad
What does missegregation of chromosomes cause?
Aneulploidy
What is disomy
2 homologous chromosomes
What is trisomy?
3 homologous chromosomes
What is monosomy?
1 chromosome
What type of aneuploidy is trisomy 21?
Down syndrome
What happens if you have trisomy 13 or trisomy 18?
Can survive birth but die shorty after
What happens in turner syndrome? (X)
Spontaneous abortions or females will have reduced height and be infertile
What happens in Klinefelter syndrome (XXY)?
Male increased height and infertile
Why is aneuploidy bad?
There is a 50% increase or decrease in gene dosage. Most genes have no defects but some are harmful which means if they are increased or decreases this could be very bad and cause death
Do small chromosomes deal with aneuploidy better?
Yes because there is less genes
Is aneuploidy in oocytes higher in humans than other mammals?
Yes
Where do aneuploidy come from?
Either mother or father or from meiosis 1 or meiosis 2
How can you tell is aneuploidy comes from the mother or father?
You can tell the origins of chromosomes by using molecular markers e.g. sequence all genomes and see where the missing or extra chromosomes is from
How can you tell that meiosis 1 failure has caused aneuploidy?
There will be 2 homologous chromosomes in the cells
How can you tell that aneuploidy has happened in meiosis 2?
The sister chromatids will not separate meaning that there will be two sister chromatids on one gamete
How can you tell homologous and sister chriamtids in gametes apart when they have swapped genes?
Look at the centromere - homologous = different coloured centromere, sister chromatids = he same coloured centromere
In what parents and what meiosis is Down syndrome commonly caused in?
Maternal meiosis 1
In what parents and meiosis is Down syndrome commonly caused by?
Maternal in meiosis 1
Recombination events influences chromosomes segregation - if there is no recombination where is it most likely there will be mis-segregation?
Meiosis 1
Recombination events influences chromosomes segregation - if there is a single recombination near a telomerewhere is it most likely there will be mis-segregation
Meiosis 1
Recombination events influences chromosomes segregation - if there is recombination need to centromere where is it most likely there will be mis-segregation
Meiosis II
Maternal age effects - does the occurrence of Down syndrome and all trisomys more common with older mothers?
Yes
Maternal age effects - why do we think this happens?
They hypothesises that the prolonged arrest seen in oocytes (from mothers birth to ovulation which can be around 40 years for some eggs or 12 for others) can cause aneuploidy
Maternal effect - how does this rest between mitosis and meiosis seen in eggs influence cohesin - the cohensin fatigue hypothesis?
Cohesin established during S phase and destroyed in anaphase.
S stage will take place before a mothers own birth and anaphase would take place once they have ovulated which could be when their 30 - this could mean the cohesin gets tired and breaks unnecessarily.
