Lecture 8 - Aneulploidy And Non-disjunction

Question 1

How could meiosis go wrong - what would happen is chromosomes didn’t recombine?

Answer 1

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

Question 2

How could meiosis go wrong - what would happen is crossing over happened to close to the telomere?

Answer 2

There’s not as much cohesin and therefore easier to lose which would cause sliding

Question 3

What would happen is cohesin isn’t protected at the centromeres?

Answer 3

Sister chromatids separate and can go to either pole. If they go to the same one this is bad

Question 4

What does missegregation of chromosomes cause?

Answer 4

Aneulploidy

Question 5

What is disomy

Answer 5

2 homologous chromosomes

Question 6

What is trisomy?

Answer 6

3 homologous chromosomes

Question 7

What is monosomy?

Answer 7

1 chromosome

Question 8

What type of aneuploidy is trisomy 21?

Answer 8

Down syndrome

Question 9

What happens if you have trisomy 13 or trisomy 18?

Answer 9

Can survive birth but die shorty after

Question 10

What happens in turner syndrome? (X)

Answer 10

Spontaneous abortions or females will have reduced height and be infertile

Question 11

What happens in Klinefelter syndrome (XXY)?

Answer 11

Male increased height and infertile

Question 12

Why is aneuploidy bad?

Answer 12

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

Question 13

Do small chromosomes deal with aneuploidy better?

Answer 13

Yes because there is less genes

Question 14

Is aneuploidy in oocytes higher in humans than other mammals?

Answer 14

Yes

Question 15

Where do aneuploidy come from?

Answer 15

Either mother or father or from meiosis 1 or meiosis 2

Question 16

How can you tell is aneuploidy comes from the mother or father?

Answer 16

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

Question 17

How can you tell that meiosis 1 failure has caused aneuploidy?

Answer 17

There will be 2 homologous chromosomes in the cells

Question 18

How can you tell that aneuploidy has happened in meiosis 2?

Answer 18

The sister chromatids will not separate meaning that there will be two sister chromatids on one gamete

Question 19

How can you tell homologous and sister chriamtids in gametes apart when they have swapped genes?

Answer 19

Look at the centromere - homologous = different coloured centromere, sister chromatids = he same coloured centromere

Question 20

In what parents and what meiosis is Down syndrome commonly caused in?

Answer 20

Maternal meiosis 1

Question 21

In what parents and meiosis is Down syndrome commonly caused by?

Answer 21

Maternal in meiosis 1

Question 22

Recombination events influences chromosomes segregation - if there is no recombination where is it most likely there will be mis-segregation?

Answer 22

Meiosis 1

Question 23

Recombination events influences chromosomes segregation - if there is a single recombination near a telomerewhere is it most likely there will be mis-segregation

Answer 23

Meiosis 1

Question 24

Recombination events influences chromosomes segregation - if there is recombination need to centromere where is it most likely there will be mis-segregation

Answer 24

Meiosis II

Question 25

Maternal age effects - does the occurrence of Down syndrome and all trisomys more common with older mothers?

Answer 25

Yes

Question 26

Maternal age effects - why do we think this happens?

Answer 26

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

Question 27

Maternal effect - how does this rest between mitosis and meiosis seen in eggs influence cohesin - the cohensin fatigue hypothesis?

Answer 27

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.