They are unicellular prokaryotes, that are lacking membrane bound organelles.
Because they take place at an atomic level and are unable to be seen by the human eye
I don't know much about it but i think it is when <span>When you crosses 2 plants of the same pure lines parentage, the resulting F1 is termed as true-breeding plants.
</span>True-breeding plants can also be produced by <span> selfing </span> (or self crossing) flowers form a pure line plant. When seeds from this fertilization are planted, they will give rise to homologous-homogeneous population.
HOPE I HELPED U ^﹏^
Because it helps them with finding new researches.