Session 4 (DNA Repair + Meiosis And Mitosis) Flashcards
What is non-disjunction?
When chromosomes don’t split and both chromatids end up in the same cell
What is aneuploidy? And what causes it?
Abnormal chromosomal no. In cell
Mitotic non-disjunction
What is mosaicism?
Presence of 2+ cell lines in an individual
How do you get mosaic karyotypes as a result of nondisjunction?
If the mutation has occurs later in division of zygote/embryo
Only some cells are affected
How do you get non mosaic karyotypes as a result of nondisjunction?
If it occurred at the 1st post zygotic division
All cells are affected
What is Robertsonian translocation?
When 2 Q arms of the same chromosome fuse together and the P arms usually fuse also but are lost, person is often phenotypically normal but their children are at risk
What are some sources of DNA damage? (5)
Endogenous- DNA replication errors, free radicals
Exogenous- UV light, ionising radiation, anti-cancer agents
What are the mitotic checkpoints?
G1- checking favourability of environment
G2- DNA checked, any damage? Is it all replicated?
Mitosis- attachment of chromosomes to spindle fibres checked
Why do checkpoints provide temporary arrest?
Provides time for DNA damage to be repaired
What occurs if DNA damage is too high?
Permanent cell cycle arrest (G0)
Apoptosis
What are the 4 types of repair?
Base (pair) excision repair- single strand breaks
Double strand repair- double strand breaks
Nucleotide excision repair- bulky adducts, intrastrand crosslinks
Mismatch repair-incorrect pairing, insertion and deletion
What gene controls cell growth and is a tumour supressor?
P53
What are heterogenous tumours?
Tumours with sub-clones, various phenotypic/morphological profiles
How can heterogenous tumours be resistant to cancer therapies?
Different sensitivity- subclones having differing response
Chemo induced mutagenesis- some treatments cause DNA damage to normal cells->mutations arise
