The nuclear DNA content of a single sperm cell in Drosophila melanogaster is approximately 0.18 picogram. What would be the expected nuclear DNA content of a primary spermatocyte in Drosophila? What would be the expected nuclear DNA content of a somatic cell (non-sex cell) in the G1 phase? What would be the expected nuclear DNA content of a somatic cell at metaphase?

Key Concepts

Haploid and Diploid Cells

In Drosophila melanogaster, sperm cells are haploid, meaning they contain one set of chromosomes, which corresponds to approximately 0.18 picogram of DNA. In contrast, somatic cells are diploid, containing two sets of chromosomes. This distinction is crucial for understanding the DNA content in different cell types during various stages of the cell cycle.

Cell Cycle Stages

The cell cycle consists of several phases, including G1, S, G2, and M (mitosis). In the G1 phase, somatic cells have a diploid DNA content, which is double that of haploid cells. During metaphase, the DNA is replicated and condensed, but the total amount of DNA remains the same as in G2, as it is still diploid, just organized differently for cell division.

DNA Replication

DNA replication occurs during the S phase of the cell cycle, where each chromosome is duplicated, resulting in two sister chromatids. This process is essential for ensuring that each daughter cell receives an identical set of chromosomes. Understanding this concept helps clarify why the DNA content of somatic cells changes between the G1 phase and metaphase, as the DNA is replicated but not yet separated.