Anaphase: Definition & Concept

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  • 0:00 What Is Anaphase?
  • 2:06 What Happens During Anaphase?
  • 2:58 What If Something Goes Wrong?
  • 5:08 Lesson Summary
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Lesson Transcript
Instructor: Angela Lynn Swafford

Lynn has a BS and MS in biology and has taught many college biology courses.

Anaphase is a very important stage of cell division. In this lesson, you can lean about the process of anaphase and what happens if something goes wrong during it.

What Is Anaphase?

Most eukaryotic cells, or those cells that have a nucleus, undergo a process called mitosis when they need to reproduce. Mitosis is the division of the nucleus. The nucleus is the structure that contains DNA, which holds genetic information.

DNA can be arranged loosely as chromatin, or it can be condensed into chromosomes. Chromosomes only become visible during mitosis. When a cell is not dividing, it is in a stage called interphase, in which chromatin is present.

To get ready for mitosis, a cell must first undergo DNA replication during interphase. This process duplicates every strand of DNA so that there are two copies of every chromosome. The two copies are called sister chromatids and are attached at the centromere. During mitosis, kinetochores will develop on the outer sides of each centromere region. Kinetochores are the attachment points for spindle fibers. Spindle fibers extend from centrioles to kinetochores and are responsible for moving chromosomes around during mitosis.

Once DNA replication is complete, nuclear division proceeds in four stages:

  1. Prophase: chromosomes become visible, nuclear envelope disappears, kinetochores and spindle fibers form
  2. Metaphase: chromosomes align in the center of the cell at the metaphase plate
  3. Anaphase: chromosomes move outwards, towards opposite poles of the cell
  4. Telophase: reverse of prophase

Once the nucleus is divided in two, the entire cell can split into two new cells in a process called cytokinesis. In cytokinesis, a cleavage furrow, or pinched-in area, forms where the metaphase plate was and splits the cell into two.

What Happens During Anaphase?

Let's take a closer look at what happens during anaphase of mitosis. Each sister chromatid of a chromosome has spindle fibers attached to it. These spindle fibers begin to shorten and pull the sister chromatids apart at the centromere. This process of is called disjunction. Now each chromatid is called a daughter chromosome or just a chromosome.

The spindle fibers continue to shorten and move towards opposite ends or poles of the cell. This causes the cell to elongate. The chromosomes during anaphase usually have a distinct V shape. There are also two distinct sets of chromosomes now, and each daughter cell will get one set.

This is a drawing of anaphase and a real photomicrograph of a cell in anaphase. Spindle fibers are green, chromosomes are blue, and kinetochores are pink.
Anaphase Drawing and Photomicrograph

What if Something Goes Wrong?

Sometimes during anaphase, chromosomes will fail to separate properly. This is called nondisjunction. Nondisjunction results in cells with abnormal numbers of chromosomes.

Look at the following image:

During anaphase, these chromosomes should have been split into two equal groups of four. Instead, one pair of sister chromatids failed to split, resulting in one cell with 5 chromosomes and one cell with 3 chromosomes.

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