Bio — Introduction to Mitosis and Cell Cycle Context + 6 more topics

Before mitosis begins, during the S phase of interphase, the DNA in the parent cell replicates. This means that each chromosome now consists of two identical copies called sister chromatids, joined together at a point called the centromere. Each sister chromatid contains one DNA molecule.

Imagine a simplified animal cell with four chromosomes depicted in our diagrams (even though humans have 46).

The main event in metaphase is the alignment of chromosomes along the metaphase plate (also known as the equatorial plate). This "plate" isn't a physical structure, but rather the imaginary plane equidistant from the two spindle poles.

Telophase marks the completion of nuclear division, bringing the separated chromosomes back under nuclear control. It's the final stage of mitosis before the cell physically divides, a process called cytokinesis (which isn't detailed here but is the next logical step).

1. Chromosomes Arrive and Decondense: The chromosomes, which were pulled to opposite poles during anaphase, reach their destinations. Once there, they start to "unwind" or decondense, becoming less tightly packed and visible (though the source implies they might still be somewhat visible in micrographs).

Prophase is the first stage of mitosis, a process that ensures genetic material is correctly divided between two new daughter cells. In animal cells, which are the focus of your source material, this stage involves several key events, even though your diagrams simplify down to just four chromosomes instead of the 46 found in humans. The different colors in your diagrams show that half of these chromosomes come from each parent.

Anaphase is a crucial stage in mitosis where the replicated genetic material is precisely divided between the future daughter cells. Prior to this, in metaphase, the chromosomes (each still consisting of two sister chromatids) aligned on the metaphase plate.

It’s important to note the change in terminology: what was one chromosome made of two chromatids becomes two individual chromosomes once they separate. If a human cell had 46 chromosomes (each made of two chromatids) before anaphase, it temporarily has 92 individual chromosomes moving to poles during anaphase.