B. Proto-oncagenes: Stimulate cell division. The P53 gene triggers the production of DNA repair enzymes and then allows the cell to pass the G1 checkpoint if the repair is succesful. If DNA is beying repair, p53 triggers enzymes that destroys the cell. If the p53 gene is mutated, the p53 protien will be non-functional. Result: DNA is not repaired and the cell cycle will not be checked at the G1 stage and the cell will replicate and potentially a malignancy will develop. If a proto-oncagene (good) mutates and does this, it is now called an oncagene (no bueno).


Meiosis- cell division that results in th eformation of 4 genetically unique haploid gametes. Occurs in 9 phases.

I. Interphase- (G1, S, G2)- the chromosomes replicate. Human:46 to 92

II. Prophase 1- The homologous chromosomes find each other and fuse together into a 4 piece structure called a tetrad. Crossing-over occurs here - The random exchange of allelic info from 1 homologue to another. This makes every piece of DNA (except x's and y's in men) unique. and is the #1 reason for genetic variability in sexually reproducing organisms.