Mitosis and Meiosis
Objectives
- Describe the difference between a DNA molecule, a chromatid, and a chromosome.
- List the stages of the cell cycle and describe what happens during each stage.
- Compare and contrast meiosis and mitosis and recognize under which conditions each occurs.
- List the stages of meiosis and mitosis and describe what happens during each.
- Predict the number of chromosomes and DNA molecules and DNA content for a cell at a given stage of meiosis or mitosis.
- Describe the consequences to the ploidy of a genome of aberrant separation of chromosomes.
Source Material
- Selected images and text modified from Open Genetics Lectures[1]. Chapter 14: Mitosis and the Cell Cycle
- Selected images and text remixed from Online Open Genetics (Nickle and Barrette-Ng), available through Biology LibreTexts[2]. Chapter 2: Chromosomes, Mitosis, and Meiosis
Introduction
Living things all have a genome, the collection of DNA used to store genetic information. But how is that genome transmitted to offspring? This module looks at the process of cell division, including maintenance of the genome from generation to generation.
As a multicellular organism grows from a single cell, every cell contains (nearly) the same genome. That means that the genetic information must be shared as new cells are made. This requires two things: the genome must be copied, and one copy of the genome must be distributed equally to each of the daughter cells as parent cells divide. The process of dividing the chromosomes among daughter cells is called mitosis. This is described as equatorial cell division since the chromosomes must be equally distributed to daughter cells.
Some organisms can reproduce asexually, solely through mitotic or equatorial division. For example, plants can be propagated from roots or cuttings. In these cases, the offspring are genetically identical to the parent.
For organisms that sexually reproduce, genetic content from two parents is combined in their offspring. But each generation has the same number of chromosomes. So sexually-reproducing organisms have an additional need for reductive cell division when they produce reproductive cells like egg or sperm. During the process of meiosis, cells are produced with only half of the genetic content – it’s called reductive cell division because the number of chromosomes has been reduced. Then, two cells with half content come together to form a fused cell with a full genome that has genetic information from both parents.
In this module, we will look first at an overview of the cell cycle, during which the cell copies its genome and prepares for cell division. We then look at the process of mitosis, which ensures faithful distribution of chromosomes to daughter cells. We compare that to the process of meiosis, or reductive cell division, which produces cells with half of a diploid genome in preparation for sexual reproduction. And, finally, we explore the consequences of errors in meiosis and mitosis.
