Describe the typical state in which chromosomal matter exists during most of interphase and what happens to the chromosomes during the S stage of interphase in preparation of mitosis.
In interphase, the nucleus is clearly visible as a membrane bound organelle containing one or more nucleoli, dense regions of the chromosomes where rRNA is synthesized. However, in their active state, when being transcribed by mRNA, individual chromosomes cannot be distinguished from each other. Instead, they appear as a tangled, granular material termed chromatin. During S stage replication, each chromosome becomes double stranded, possessing two identical chromatids held together at their centers by a centromere. The ends of each chromatid are called telomeres. Although the cell still contains the diploid number (2N) of chromosomes, the double-stranded chromosomes are ready for division into two complete copies of the genome.
