Meiosis & Mitosis i

Question 1

What is the repeating sequence of a telomere?

Answer 1

TTAGGG

Question 2

What is centromere?

Answer 2

It links sister chromatids and consists of repetitive sequences

Question 3

What are the names for the position of a centromere on the chromosome and what do they mean?

Answer 3

Metacentric (middle)
Submetacentric (longer q arm than p arm)
Acrocentric (much longer q arm than p arm)
Telocentric (no p arm, not present in humans normally)

Question 4

What are the sizes of the chromosomes? (relative to each other)

Answer 4

Decreasing up to 21, 22 is larger
X is a C group
Y is a G group

Question 5

How are chromosomes grouped?

Answer 5

A3, B2, C7, D3, E3, F2, G2, X, Y

Question 6

Which protein recognises and binds the centromere?

Answer 6

Kinetochore

Question 7

What is the line down the middle of the cell called?

Answer 7

Metaphase plate

Question 8

What is a pair of homologous chromosomes called?

Answer 8

Tetrad or the bivalent forms

Question 9

What are the differences between spermatogenesis and oogenesis?

Answer 9

1 spermatocyte produces 4 sperm, takes 60 days

1 oocyte produces 1 ovum and 3 polar bodies, takes 12-50 years as it finishes meiosis at fertilisation

Question 10

What is the karyotype of a male with Down’s syndrome?

Answer 10

47,XY,+21

Question 11

How does Down’s syndrome occur?

Answer 11

Nondisjunction in mitosis leads to aneuploidy

Question 12

When is non-disjunction more dangerous in meiosis?

Answer 12

Meiosis I, as this results in no normal zygotes whereas if it was in Meiosis II it results in 2 normal zygotes out of 4

Question 13

How many possibilities for random assortment are there?

Answer 13

2^n (2^23 in normal humans)

Question 14

What is stage G0 in the cell cycle?

Answer 14

If cells go into this state they stop getting signals to divide again, e.g. neurones
Sometimes they can return to the cell cycle

Question 15

Which gene starts male development?

Answer 15

SRY

Question 16

What is an anaphase leg?

Answer 16

When the chromatids are not pulled apart properly so one chromatid stays in the middle

Question 17

What can repetitive DNA lead to?

Answer 17

Fork slippage, due to DNA replication stress

Question 18

What is Huntington’s disease caused by?

Answer 18

When DNA is replicating, DNA replication stress can cause fork slippage in a repetitive DNA sequence, so in HD extra CAG’s are added (glutamine residue); this is called a trinucleotide repeat disorder, or trinucleotide expansion. If there are increased CAG repeats it leads to a mutated Huntington protein, leading to neurone degeneration, mainly affecting the basal ganglia.

Question 19

What are the three ways DNA replication stress can affect DNA replication?

Answer 19

Replication machinery defects ( DNA polymerase, DNA helicase, sliding clamp)
Replication fork progression hindrance (Ribonucleotide incorporation, fragile sites, repetitive DNA, transcription)
Defects in response pathways (sensors, transducers, effectors)

Question 20

What outcomes can there be in repose to DNA damage?

Answer 20

Senescence (permanent cel cycle arrest), proliferation (repair), apoptosis (death)

Question 21

Which DNA damage type is most dangerous to repair?

Answer 21

Interstrand cross-links and double-stranded breaks, as both strands have to be cut

Question 22

How do PARP inhibitors work?

Answer 22

PARP1 is a protein which repairs single strand breaks in DNA, so when PARP inhibitors are given it causes double strand breaks down the line of replication. BRCA1 & 2 are proteins which repair double strand breaks by error-free homologous recombinational repair. Therefore, using PARP inhibitors on tumours with BRCA1 & 2 mutations causes those cells to die, whilst normal cells don’t have this mutation so they can be repaired