How does self-pollination maintain genetic purity if meiosis causes crossing over?

[chound]

My book says self pollination maintains the parental characters or purity of the race indefinitely and is used to maintain pure lines for hybridization experiments.

How can that be true. Coz, meiosis takes place in micro & mega spore mother cells. So there is crossing over which will lead to variation right?

 

[Moonbear]

Self-pollination reduces variation, but does not entirely eliminate it (due to crossing over and segregation of chromosomes during meiosis, as you have indicated), unless the parent is already homozygous for a trait. If one is only interested in studying limited traits, then it's possible to breed plants that are homozygous and then preserve those homozygous traits through continual inbreeding (self-pollination).