The synaptonemal complex appears
A. Between homologous chromosomes
B. In the zygotene stage
C. Composed of DNA + Protein
D. All of the above

Hint: A protein structure that is formed between homologous chromosomes during meiosis is called a synaptonemal complex. It is required for synapsis and recombination between homologous chromosomes during meiosis I in eukaryotes.

Complete Answer:
The synaptonemal complex was first visualized by Moses and Fawcett in 1956. The fully formed complex is a zipper-like tripartite structure that is so protein-rich that it can be observed on spread preparations under light-phase microscopy. It is formed by two lateral elements, mainly formed by SYCP3 and secondarily by SYCP2.

Let us analyze the correct answer,
- Option A: This complex is formed between homologous chromosomes which are two pairs of sister chromatids. Therefore, this statement is correct.
- Option B: The synaptonemal complex begins to form during the zygotene phase of Prophase I in the first division in Meiosis and it completes in the pachytene phase. Thus, this statement is correct as well.
- Option C: The complex is a protein structure composed of DNA and thus this statement is correct as well.
- Option D: Since all the above options are correct, this is the correct option.

Thus, the correct option is D. All of the above.

Note: The synaptonemal complex is two parallel aligned proteinaceous chromosome cores of a pair of homologous chromosomes at the prophase of meiosis. The cores are in the order of 60 to 100 nm wide, lie about 100 nm apart, and are interconnected by transverse filaments.