Question

When do the chromosomal strands become double in (1) a somatic cell and (2) a pollen mother cell (microsporocyte)? Cite and discess the evidence for the answer.

Answer 1

1. Somatic cells:

• In these cells, the DNA replication takes place during the S phase which occurs between the G1 phase and the G2 phase of the cell cycle.
• During the S phase, each of the original single-stranded chromosomes is replicated which results in the formation of identical sister chromatids which remain joined at a region called the centromere.
• These sister chromatids forms the double-stranded chromosomes.
• This process ensures that each daughter cell produced during the cell division receives an exact copy of the genetic material.
• Evidence for the timing of DNA replication in somatic cells can be found in various scientific literature which includes a notable study i.e.,  "DNA replication determines timing of mitosis by restricting CDK1 and PLK1 activation" provides insights into the coordination of cell division and DNA replication in somatic cells.

2. Pollen mother cells (microsporocytes):

• In the microsporocytes, the are cells involved in the formation of pollen grains during plant reproduction, DNA replication occurs during meiosis.
• DNA replication inmicrosporocytes specifically takes place during the S phase of meiosis I.
• Evidence for the timing of DNA replication in  microsporocytes is found in studies focusing on plant reproductive biology.
•  The notable study i.e., "Replication timing in cotton nuclei - The exclusively centromeric localization of the early replicating chromosome A" discusses the replication patterns and timing during meiosis in cotton microsporocytes.
• The notable studies mentioned above are a general understanding of the timing of DNA replication in somatic cells and microsporocytes, but there may be additional research and evidence available for the specific cell types or species.

• The DNA replication, resulting in the formation of double-stranded chromosomes occurs at specific stages in the cell cycle for both of the somatic cells and pollen mother cells i.e.,microsporocytes.