Lecture 4- Meiosis Flashcards
2 processes by which meiosis generates genetic differences
crossing over
random segregation
how does pre-meiotic S phase differ from pre-mitotic S phase?
different CDKs and cohesins are used
what happens in prophase I
crossing over and recombination
what happens in anaphase I
separation of homologous chromosomes
when do chromatids separate?
anaphase II
developmental stage of female oocytes at birth
prophase I
what brings homologous chromosome sequences into proximity?
O cohesin by alignment mechanisms
chiasmata
sites of recombination
synaptonemal complex
a mechanism of alignment, in which 2 chromosomes have points compared and aligned by filaments in a ladder-like structure. this then allows the spreading of alignment down a chromosome
horsetail movements
aligning telomeres, then alignment can happen automatically- joined at a single point (spindle pole body) like a loop, then ‘straightened out’
mechanism of recombination
double strand break created with Spo11, resection to make a 3’ end
the 3’ end can then invade the other chromosome- aided by Rad51, Dmc1
formation of a holliday junction
resolution of the jumble by resolvases
criteria for onset of anaphase
correct tension of cohesin links with microtubules at the kinetochore
why is it better dor sister chromatids to behave as a single unit?
attachment to the spindle can occur incorrectly, leading to inappropriate segregation of homologs
how do sister kinetochores come to behave as a single unit?
monopolins, attach the chromatids at the kinetochore
important proteins at metaphase I
cohesin- but only at the kinetochores, it is lost at the ‘arms’
shugoshin- protects the cohesin at the kinetochore by recruiting phosphotase
