Question

What is the nature of chromosomes that align themselves on the metaphase plate in metaphase 1?

Answer 1

homologous chromosomes, in tetrads

Answer 2

If I might extend the correct answer given above: the chromosomes are heavily condensed compared to their state during the rest of the cell cycle. The metaphase spreads which get stained to give the characteristic banding patterns shown in text books are examples of the condensed state. Note that transcription is far less likely in this state than during interphase when the chromatin is in a more relaxed state.

Having said that, the chromatin in interphase is still highly condensed, so that all the genetic information can be fitted into a cell. It's just not as condensed as in metaphase chromosomes. There's more about it here:

http://en.wikipedia.org/wiki/Chromosome#Metaphase_chromatin_and_division

Answer 3

pair of tetrads facing opposite poles