Show Like mitosis, meiosis is a form of eukaryotic cell division. However, these two processes distribute genetic material among the resulting daughter cells in very different ways. Mitosis creates two identical daughter cells that each contain the same number of chromosomes as their parent cell. In contrast, meiosis gives rise to four unique daughter cells, each of which has half the number of chromosomes as the parent cell. Because meiosis creates cells that are destined to become gametes (or reproductive cells), this reduction in chromosome number is critical — without it, the union of two gametes during fertilization would result in offspring with twice the normal number of chromosomes! Apart from this reduction in chromosome number, meiosis differs from mitosis in yet another way. Specifically, meiosis creates new combinations of genetic material in each of the four daughter cells. These new combinations result from the exchange of DNA between paired chromosomes. Such exchange means that the gametes produced through meiosis exhibit an amazing range of genetic variation. Finally, unlike mitosis, meiosis involves two rounds of nuclear division, not just one. Despite this fact, many of the other events of meiosis are similar to those that occur in mitosis. For example, prior to undergoing meiosis, a cell goes through an interphase period in which it grows, replicates its chromosomes, and checks all of its systems to ensure that it is ready to divide. Like mitosis, meiosis also has distinct stages called prophase, metaphase, anaphase, and telophase. A key difference, however, is that during meiosis, each of these phases occurs twice — once during the first round of division, called meiosis I, and again during the second round of division, called meiosis II.
What happens during meiosis I?
As previously mentioned, the first round of nuclear division that occurs during the formation of gametes is called meiosis I. It is also known as the reduction division because it results in cells that have half the number of chromosomes as the parent cell. Meiosis I consists of four phases: prophase I, metaphase I, anaphase I, and telophase I.
Prophase I
During prophase I, the chromosomes condense and become visible inside the nucleus. Because each chromosome was duplicated during the S phase that occurred just before prophase I, each now consists of two sister chromatids joined at the centromere. This arrangement means that each chromosome has the shape of an X. Once this chromosomal condensation has occurred, the members of each chromosome pair (called homologous chromosomes, because they are similar in size and contain similar genes), align next to each other. At this point, the two chromosomes in each pair become tightly associated with each other along their lengths in a process called synapsis. Then, while the homologous chromosomes are tightly paired, the members of each pair trade adjacent bits of DNA in a process called crossing over, also known as recombination (Figure 1). This trading of genetic material creates unique chromosomes that contain new combinations of alleles. At the end of prophase I, the nuclear membrane finally begins to break down. Outside the nucleus, the spindle grows out from centrosomes on each side of the cell. As in mitosis, the microtubules of the spindle are responsible for moving and arranging the chromosomes during division.
Metaphase I
Anaphase I
Telophase I
Interkinesis
At this point, the first division of meiosis is complete. The cell now rests for a bit before beginning the second meiotic division. During this period, called interkinesis, the nuclear membrane in each of the two cells reforms around the chromosomes. In some cells, the spindle also disintegrates and the chromosomes relax (although most often, the spindle remains intact). It is important to note, however, that no chromosomal duplication occurs during this stage.
What happens during meiosis II?
During meiosis II, the two cells once again cycle through four phases of division. Meiosis II is sometimes referred to as an equational division because it does not reduce chromosome number in the daughter cells — rather, the daughter cells that result from meiosis II have the same number of chromosomes as the "parent" cells that enter meiosis II. (Remember, these "parent" cells already have half the number of chromosomes of the original parent cell thanks to meiosis I.)
Prophase II
As prophase II begins, the chromosomes once again condense into tight structures, and the nuclear membrane disintegrates. In addition, if the spindle was disassembled during interkinesis, it reforms at this point in time.
Metaphase II
Anaphase II
Telophase II
Why is meiosis important?
Alternate version of this benchmark for students with significant cognitive disabilities.
Vetted resources educators can use to teach the concepts and skills in this benchmark.
Comparing Mitosis and Meiosis: Compare and contrast mitosis and meiosis in this interactive tutorial. You'll also relate them to the processes of sexual and asexual reproduction and their consequences for genetic variation.
Vetted resources students can use to learn the concepts and skills in this benchmark.
Reproduction Strategies: Explore consequences and challenges of reproductive strategies of sea anemones. Type: Original Student Tutorial Comparing Mitosis and Meiosis: Compare and contrast mitosis and meiosis in this interactive tutorial. You'll also relate them to the processes of sexual and asexual reproduction and their consequences for genetic variation. Type: Original Student Tutorial
Spermatogenesis: Spermatogenesis is the process in which spermatozoa are produced from male primordial germ cells by way of mitosis and meiosis. This tutorial will help the learners to understand the process of spermatogenesis. Type: Tutorial Unique Features of Meiosis: This tutorial will help you to understand the three unique features of meiosis and how meiosis is related to genetic inheritance. Type: Tutorial Comparison of Meiosis and Mitosis: This tutorial will help students understand the differences between meiosis and mitosis. The processes differ in two fundamental ways. Meiosis has two rounds of genetic separation and cellular division while mitosis only has one of each. In meiosis, homologous chromosomes separate leading to daughter cells that are not genetically identical. In mitosis, the daughter cells are identical to the parent as well as to each other. Type: Tutorial Comparison of Meiosis and Mitosis: This tutorial will help you compare meiosis and mitosis. It discusses the similarities that are found in both, as well as the fundamental differences between the two types of cell division. Type: Tutorial Meiosis Tutorial: This online tutorial is designed to help students understand the events that occur in process of meiosis. Type: Tutorial
Mitosis and meiosis are processes involved in cellular reproduction. Which of the following describes and event that results from mitosis but NOT meiosis? A. two stages of cell division B. replication of cellular genetic material C. daughter cells that are identical to the parent cell D. four daughter cells that are produced from each parent cell CLICK HERE FOR ANSWER
How are sexual reproduction and asexual reproduction different from each other? A. sexual reproduction requires two parents and asexual reproduction requires only one parent B. asexual reproduction requires two parents and sexual reproduction requires only one parent C. mutation rates are lower in sexual reproduction than in asexual reproduction D. asexual reproduction occurs only in multicellular organisms CLICK HERE FOR ANSWER
Which type of reproduction leads to increased genetic variation on a population? A. Parthenogenesis B. asexual reproduction C. Sexual reproduction D. Vegetative reproduction CLICK HERE FOR ANSWER
Which of the following phrases best describes cancer? A. absence of cyclins in the DNA B. miltiple gene mutations on a chromosome of DNA C. uncontrolled cell growth caused by mutations in genes that control the cell cycle D. presence of genetic defects caused by hereditary disorders CLICK HERE FOR ANSWER
Which of the following phases of mitosis is represented by the diagram below?  A. prophase B. metaphase C. anaphase D. telophase CLICK HERE FOR ANSWER
A scientist wants to change the DNA of a sexually reproducing organism and have the new DNA present in every cell of the organism. In order to do this after fertilization, she would change the DNA in which of the following? A. zygote B. placenta C. testes of the father D. ovaries of the mother CLICK HERE FOR ANSWER
Which row in the chart below indicates the correct process for each event indicated? A. row 1 B. row 2 C. row 3 D. row 4 CLICK HERE FOR ANSWER
The diagram below shows a cellular process that occurs in organisms. What is the name of this process? A. meiosis B. mitosis C. endocytosis D. phagocytosis CLICK HERE FOR ANSWER
The diagram below shows homologous chromosomes during prophase I of meiosis. Which of the following correctly describes the process being illustrated? A. mutation in which the DNA content of the gene is altered B. segregation of sister chromatids C. condensation and segregation of alleles D. crossing-over in which alleles are exchanged CLICK HERE FOR ANSWER
Which of the following best describes meiosis? A. It is carried out in all tissues that require cell replacement. B. It occurs only in cells in the reproductive structures of organisms. C. It happens in all tissues except the brain and spinal cord. D. It is the first stage of mitosis. CLICK HERE FOR ANSWER
The diagram below shows two strawberry plants. Plant 2 is produced asexually from Plant 1. If the leaf cells of Plant 1 have 56 chromosomes, how many chromosomes will be found in the leaf cells of Plant 2? A. 14 B. 28 C. 56 D. 112 CLICK HERE FOR ANSWER
Mitosis, Meiosis, and Sexual Reproduction
Mitosis vs Meiosis
General Biology - Sections 5.1 and 5.2, pgs. 134-143, and Sections 6.1 and 6.2, pgs. 168-176 Honors Biology - Sections 10.1 and 10.2, pgs. 234-244, and Section 11.4 pgs. 275-285 |
Which of the following describes an event that results from mitosis but not meiosis?
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