The diploid number of the hypothetical animal Geneticus introductus is 2n = 36. Each diploid nucleus contains 3 ng of DNA in G₁.

Explain why a somatic cell of Geneticus introductus has the same number of chromosomes and the same amount of DNA at the beginning of mitotic prophase as one of these cells does at the beginning of prophase I of meiosis.

Verified step by step guidance

1. <span>Step 1: Understand the cell cycle phases involved. In both mitosis and meiosis, cells undergo a preparatory phase called interphase, which includes the G₁, S, and G₂ phases. During the S phase, DNA replication occurs, doubling the DNA content while the chromosome number remains the same.</span>
2. <span>Step 2: Consider the chromosome and DNA content at the beginning of mitotic prophase. After the S phase, each chromosome consists of two sister chromatids, but the number of chromosomes remains the same (2n = 36). The DNA content, however, has doubled to 6 ng.</span>
3. <span>Step 3: Analyze the chromosome and DNA content at the beginning of prophase I of meiosis. Similar to mitosis, meiosis begins after interphase, where DNA replication has occurred. Thus, at the start of prophase I, each chromosome also consists of two sister chromatids, maintaining the chromosome number at 2n = 36 and the DNA content at 6 ng.</span>
4. <span>Step 4: Compare the two processes. Both mitotic prophase and prophase I of meiosis start with the same chromosome number and DNA content because they both follow a similar interphase where DNA replication occurs, but no change in chromosome number happens.</span>
5. <span>Step 5: Conclude the explanation. The key reason for the similarity in chromosome number and DNA content at these stages is the replication of DNA during the S phase of interphase, which precedes both mitosis and meiosis.</span>

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 Geneticus introductus. This means that each somatic cell contains two sets of chromosomes, one inherited from each parent. Understanding the diploid number is crucial for comprehending how genetic information is organized and passed on during cell division.

Mitosis vs. Meiosis

Mitosis is the process of cell division that results in two identical daughter cells, each with the same number of chromosomes as the parent cell. In contrast, meiosis is a specialized form of cell division that reduces the chromosome number by half, producing gametes. At the beginning of mitotic prophase, the somatic cell has the same chromosome number and DNA content as it does at the start of prophase I of meiosis, as both processes begin with diploid cells.

DNA Content in Cell Cycle

The amount of DNA in a cell varies throughout the cell cycle. In the G₁ phase, a diploid cell contains a specific amount of DNA (3 ng in this case), which is duplicated during the S phase, leading to double the DNA content before mitosis or meiosis. However, at the beginning of mitotic prophase and prophase I of meiosis, the DNA content is effectively the same because both processes start with cells that have completed DNA replication.