Asexual vs. SexualReproduction

Douglas Wilkin, Ph.D.Jean Brainard, Ph.D.

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Printed: January 2, 2015

AUTHORSDouglas Wilkin, Ph.D.Jean Brainard, Ph.D.

www.ck12.org Chapter 1. Asexual vs. Sexual Reproduction

CHAPTER 1 Asexual vs. SexualReproduction

• Distinguish cell division from asexual reproduction.• Compare and contrast asexual and sexual reproduction.• Distinguish binary fission, fragmentation, and budding.• Define zygote.• Differentiate between haploid and diploid.

One parent or two?

That is the main difference between sexual and asexual reproduction. Sexual reproduction just means combininggenetic material from two parents. Asexual reproduction produces offspring genetically identical to the one parent.

Reproduction: Asexual vs. Sexual

Cell division is how organisms grow and repair themselves. It is also how many organisms produce offspring. Formany single-celled organisms, reproduction is a similar process. The parent cell simply divides to form two daughtercells that are identical to the parent. In many other organisms, two parents are involved, and the offspring are notidentical to the parents. In fact, each offspring is unique. Look at the family in Figure 1.1. The children resembletheir parents, but they are not identical to them. Instead, each has a unique combination of characteristics inheritedfrom both parents.

Reproduction is the process by which organisms give rise to offspring. It is one of the defining characteristics ofliving things. There are two basic types of reproduction: asexual reproduction and sexual reproduction.

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FIGURE 1.1Family Portrait: Mother, Daughter, Father,and Son. Children resemble their parents,but they are never identical to them. Doyou know why this is the case?

Asexual Reproduction

Asexual reproduction involves a single parent. It results in offspring that are genetically identical to each otherand to the parent. All prokaryotes and some eukaryotes reproduce this way. There are several different methods ofasexual reproduction. They include binary fission, fragmentation, and budding.

• Binary fission occurs when a parent cell splits into two identical daughter cells of the same size.• Fragmentation occurs when a parent organism breaks into fragments, or pieces, and each fragment develops

into a new organism. Starfish, like the one in Figure 1.3, reproduce this way. A new starfish can develop froma single ray, or arm. Starfish, however, are also capable of sexual reproduction.

• Budding occurs when a parent cell forms a bubble-like bud. The bud stays attached to the parent cell whileit grows and develops. When the bud is fully developed, it breaks away from the parent cell and forms a neworganism. Budding in yeast is shown in Figure 1.3.

Asexual reproduction can be very rapid. This is an advantage for many organisms. It allows them to crowd outother organisms that reproduce more slowly. Bacteria, for example, may divide several times per hour. Under idealconditions, 100 bacteria can divide to produce millions of bacterial cells in just a few hours! However, most bacteriado not live under ideal conditions. If they did, the entire surface of the planet would soon be covered with them.Instead, their reproduction is kept in check by limited resources, predators, and their own wastes. This is true ofmost other organisms as well.

Sexual Reproduction

Sexual reproduction involves two parents. As you can see from Figure 1.4, in sexual reproduction, parents producereproductive cells—called gametes—that unite to form an offspring. Gametes are haploid cells. This means theycontain only half the number of chromosomes found in other cells of the organism. Gametes are produced by atype of cell division called meiosis, which is described in detail in a subsequent concept. The process in which twogametes unite is called fertilization. The fertilized cell that results is referred to as a zygote. A zygote is diploidcell, which means that it has twice the number of chromosomes as a gamete.

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www.ck12.org Chapter 1. Asexual vs. Sexual Reproduction

FIGURE 1.2Binary Fission in various single-celled or-ganisms (left). Cell division is a relativelysimple process in many single-celled or-ganisms. Eventually the parent cell willpinch apart to form two identical daughtercells. In multiple fission (right), a multinu-cleated cell can divide to form more thanone daughter cell. Multiple fission is moreoften observed among protists.

Mitosis, Meiosis and Sexual Reproduction is discussed at http://www.youtube.com/watch?v=kaSIjIzAtYA .

MEDIAClick image to the left or use the URL below.URL: http://www.ck12.org/flx/render/embeddedobject/275

Summary

• Asexual reproduction involves one parent and produces offspring that are genetically identical to each otherand to the parent.

• Sexual reproduction involves two parents and produces offspring that are genetically unique.

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FIGURE 1.3Starfish reproduce by fragmentation and yeasts reproduce by budding. Both are types of asexual reproduction.

FIGURE 1.4Cycle of Sexual Reproduction. Sexualreproduction involves the production ofhaploid gametes by meiosis. This is fol-lowed by fertilization and the formation ofa diploid zygote. The number of chromo-somes in a gamete is represented by theletter n. Why does the zygote have 2n, ortwice as many, chromosomes?

• During sexual reproduction, two haploid gametes join in the process of fertilization to produce a diploidzygote.

• Meiosis is the type of cell division that produces gametes.

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www.ck12.org Chapter 1. Asexual vs. Sexual Reproduction

Explore More

Use this resource to answer the questions that follow.

• Sexual vs. Asexual Reproduction at http://learn.genetics.utah.edu/content/variation/reproduction/ .

1. How do the offspring of asexual reproduction compare to the parent?2. How do the offspring of sexual reproduction compare to the parents?3. How do the following organism reproduce?

a. brittle starsb. Salmonellac. cactusd. sunflowere. garden strawberryf. coast redwood treeg. grizzly bear

Review

1. What are three types of asexual reproduction?2. Define gamete and zygote. What number of chromosomes does each have (in humans)?3. What happens during fertilization?4. Compare and contrast asexual and sexual reproduction.

References

1. Image copyright Juan Carlos Tinjaca, 2014. A family portrait shows children resemble their parents but arenot identical to them . Used under license from Shutterstock.com

2. Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation. Illustrates binary fission in single-celled organisms and multiple fission in multinucleated cells . CC BY-NC 3.0

3. Starfish: Flickr:amanderson2; Yeast: Zappy’s. Starfish and yeasts are examples of organisms that reproduceasexually . Starfish: CC BY 2.0; Yeast: CC BY-NC 3.0

4. Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation. An illustrative overview of the sexual reproduction process . CC BY-NC 3.0

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