Meiosis & Mitosis i Flashcards
What is the repeating sequence of a telomere?
TTAGGG
What is centromere?
It links sister chromatids and consists of repetitive sequences
What are the names for the position of a centromere on the chromosome and what do they mean?
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)
What are the sizes of the chromosomes? (relative to each other)
Decreasing up to 21, 22 is larger
X is a C group
Y is a G group
How are chromosomes grouped?
A3, B2, C7, D3, E3, F2, G2, X, Y
Which protein recognises and binds the centromere?
Kinetochore
What is the line down the middle of the cell called?
Metaphase plate
What is a pair of homologous chromosomes called?
Tetrad or the bivalent forms
What are the differences between spermatogenesis and oogenesis?
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
What is the karyotype of a male with Down’s syndrome?
47,XY,+21
How does Down’s syndrome occur?
Nondisjunction in mitosis leads to aneuploidy
When is non-disjunction more dangerous in meiosis?
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
How many possibilities for random assortment are there?
2^n (2^23 in normal humans)
What is stage G0 in the cell cycle?
If cells go into this state they stop getting signals to divide again, e.g. neurones
Sometimes they can return to the cell cycle
Which gene starts male development?
SRY
What is an anaphase leg?
When the chromatids are not pulled apart properly so one chromatid stays in the middle
What can repetitive DNA lead to?
Fork slippage, due to DNA replication stress
What is Huntington’s disease caused by?
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.
What are the three ways DNA replication stress can affect DNA replication?
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)
What outcomes can there be in repose to DNA damage?
Senescence (permanent cel cycle arrest), proliferation (repair), apoptosis (death)
Which DNA damage type is most dangerous to repair?
Interstrand cross-links and double-stranded breaks, as both strands have to be cut
How do PARP inhibitors work?
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
