1. a mouse's toes undergo apoptosis during a late stage of development. due to signaling protein: BMP4 that instructs cells in webbing to undergo apoptosis
- both embryos express BMP4 gene but differ in expression of gene Gremlin- ducks
-- Gremlin protein inhibits BMP4 from signaling for apoptosis= webbed foot
2. Cyclin is a family of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase