In mitosis, the prophase is further understood by dividing it into the given sub-stages:
1.Leptotene :
In this stage the nucleus enlarges in size in the chromosome. The chromosomes appear thin, thread-like and single-stranded in this stage. They have swollen or beaded structures along their length and their ends appear converged towards one side of the nucleus called bouquet.
2.Zygotene:
In this stage, the identical chromosomes come together and form bivalent or homologous pairs. Further, ...
Yes, a vector which has zero magnitude is also a vector in case of two vectors travelling in opposite directions with equal magnitudes. At this case, the resultant vector has zero magnitude but it is still a vector. We call it a null vector.

The Rh factor(the Rhesus factor or Rh antigen), is a protein that can be found on the surface of red blood cells. It is one of the most important blood group systems in human blood typing. The presence or absence of the Rh factor is denoted as either Rh-positive (+) or Rh-negative (-).
Fun fact: The Rh factor is named after the Rhesus monkey, in which the protein was first discovered.