Why doesn't a spider get stuck in its own web?

spiders don't come into contact with their webs all at once. Instead, they move nimbly along the strands of their webs with only the hairs on the tips of their legs making contact with the sticky threads.  

One hypothesis, that spiders simply skip over the sticky threads, has been more or less discredited. In fact, orb-weavers sweep their hind legs across the goo hundreds or thousands of times as they make their webs. They also brush their bodies against the drops while they're subduing prey. Hope I helped

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.