If you look through a microscope and see a cell with chromosomes lined up two by two, what stage of cellular reproduction must you be looking at?

1. mitosis only
2. meiosis i only
3. meiosis ii only
4. either mitosis or meiosis i
5. either meiosis i or meiosis ii

2. meiosis I only

Explanation:

During the zygotene stage of prophase-I of meiosis-I, homologous chromosomes synapse and are paired up. These paired homologous chromosomes are called bivalents. These paired homologous chromosomes align themselves at the equatorial plate of the cell during metaphase-I. Therefore, when observed through a microscope, cells are shown lined up two by two. During meiosis-II and mitosis, individual chromosomes with two sister chromatids are aligned at the cell's equator in metaphase.

d.

explanation:

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.