The diploid number of the hypothetical animal Geneticus introductus is 2n = 36. Each diploid nucleus contains 3 ng of DNA in G₁.
What amount of DNA is contained in each nucleus at the end of the S phase?

Verified step by step guidance

1. Understand the problem: The diploid number (2n) of the organism is 36, and the DNA content in G₁ phase is 3 ng. The question asks for the DNA content at the end of the S phase, where DNA replication occurs.
2. Recall that during the S phase of the cell cycle, DNA replication takes place, doubling the amount of DNA in the nucleus. However, the chromosome number (2n = 36) remains the same because no cell division occurs during this phase.
3. Since the DNA content in G₁ is 3 ng, and the S phase doubles the DNA content, the DNA content at the end of the S phase will be twice the amount present in G₁.
4. Set up the calculation: Multiply the DNA content in G₁ (3 ng) by 2 to determine the DNA content at the end of the S phase. Use the formula: $\mathrm{DNA}=2\times 3\mathrm{ng}$.
5. Conclude that the DNA content at the end of the S phase is double the G₁ content, which reflects the completion of DNA replication.

Key Concepts

Diploid Number

The diploid number (2n) refers to the total number of chromosomes in a somatic cell, which in this case is 36 for the animal Geneticus introductus. This means that there are 18 pairs of homologous chromosomes, with one set inherited from each parent. Understanding the diploid number is crucial for determining the genetic content of the organism.

DNA Replication

DNA replication is the process by which a cell duplicates its DNA before cell division. During the S phase of the cell cycle, each chromosome is replicated, resulting in two sister chromatids for each chromosome. This means that the total amount of DNA in the nucleus doubles, which is essential for ensuring that each daughter cell receives an identical set of chromosomes.

S Phase

The S phase, or synthesis phase, is a part of the cell cycle where DNA replication occurs. It follows the G₁ phase and precedes the G₂ phase. During this phase, the amount of DNA in the nucleus increases as each chromosome is copied, leading to a temporary state where the amount of DNA is twice that of the G₁ phase, which is critical for proper cell division.