Cellular Biology | Class 22: Cell Cycle 4

Mad2 initial localization

In the nuclear membrane before envelope disassembly

Mad2 localization after nuclear envelope breakdown

Associates with unattached kinetochores

MCC (Mitotic Checkpoint Complex) components

Mad2; Bub3; BubR1; and Cdc20

Target of the Spindle Assembly Checkpoint

APC/C

Function of the MCC

Blocks APC/C activation to delay anaphase

Effect of unattached kinetochores on MCC

Catalyze the formation of the MCC to inhibit the cycle

Meiosis chromosome reduction

Reduces chromosome number by half (from 2n to 1n)

Events unique to Meiotic Prophase I

Homolog pairing; synapsis; and recombination (crossing over)

Meiosis I segregation

Homologous chromosomes separate

Meiosis II segregation

Sister chromatids separate

Gene X experimental role in meiosis

Required for crossover formation and homolog connection

Gene Y experimental role in meiosis

Required for sister chromatid cohesion

Co-orientation in Meiosis I

Sister kinetochores attach to spindle microtubules from the same pole

Shugoshin function

Protects centromeric cohesin from cleavage during Meiosis I

Mechanism of Shugoshin

Recruits PP2A to counteract Rec8 phosphorylation

Rec8 cleavage condition

Must be phosphorylated to be cleaved by Separase

Trisomy 21 cause

Errors in meiosis (nondisjunction) often linked to maternal age

Human oocyte status in Meiosis II

Arrested at Metaphase II until fertilization by sperm