During which phase of meiosis are spindle fibers fully developed?

The correct phase during which spindle fibers are fully developed is Prophase 2. In meiosis, particularly during Prophase 2, the cell prepares for the second meiotic division. During this phase, the nuclear envelope begins to break down, and the spindle apparatus is re-formed from the microtubules. As the spindle fibers become fully developed, they extend from the centrosomes and prepare to attach to the chromosomes which will align in Metaphase 2.

In contrast, during Prophase 1, the spindle apparatus begins to form, but it is not fully developed at that stage. The primary focus of Prophase 1 is on the pairing of homologous chromosomes and crossing over, which doesn't focus on the complete development of spindle fibers. Metaphase 2 involves the alignment of chromosomes along the equatorial plane, but the spindle fibers would have been fully developed prior to this as part of Prophase 2 preparations. Telophase 1 marks the end of the first meiotic division when the cell divides, but by then, the emphasis is shifting away from spindle fiber development to the reformation of the nuclear envelope.