Question

1. what two structures make up a single replicated chromosome?
2. in model 1, how many replicated chromosomes does the cell contain during prophase?

Explanation:

Question 3

A replicated chromosome is made up of two sister chromatids. These are identical copies of a chromosome that are joined together at the centromere, formed during DNA replication in the S - phase of the cell cycle.

Step 1: Recall the concept of chromosome replication

During the S - phase of the cell cycle, each chromosome (composed of a single DNA molecule) replicates to form a replicated chromosome with two sister chromatids. The number of replicated chromosomes is equal to the number of chromosomes in the diploid cell (before replication, the cell has n or 2n chromosomes, after replication, the number of replicated chromosomes is still n or 2n, but each has two chromatids).

Step 2: Apply to a typical model (example)

If we take a model cell with 2n = 4 (diploid, 4 chromosomes), after S - phase (replication), in prophase, the number of replicated chromosomes is 4 (each chromosome is now a replicated chromosome with two chromatids).

Answer:

Two sister chromatids make up a single replicated chromosome.

Question 4

To answer this, we need to know the context of "Model 1" (usually a cell cycle or mitosis/meiosis model). In a typical diploid cell model (e.g., for human cells, 2n = 46 in interphase before mitosis), during prophase (after S - phase where DNA replicates), the number of replicated chromosomes (each with two sister chromatids) is equal to the number of chromosomes in the diploid cell. If we assume a common model like a cell with 4 chromosomes in diploid state (2n = 4), after replication in S - phase, in prophase, the number of replicated chromosomes is still 4 (each chromosome is now a replicated chromosome with two chromatids). But if we take a human cell example, a human cell has 46 chromosomes in diploid state. After S - phase (replication), during prophase of mitosis, the cell has 46 replicated chromosomes (each replicated chromosome has two sister chromatids). However, since the "Model 1" is not specified, if we consider a simple model with, say, 2 pairs of homologous chromosomes (total 4 chromosomes in diploid), after replication, in prophase, the number of replicated chromosomes is 4.