Lesson 1: Asexual vs. Sexual
Reproduction
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
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Printed: October 19, 2014
AUTHORS
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Lesson 1: Asexual vs. Sexual Reproduction
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Lesson 1: Asexual vs.
Sexual Reproduction
• Compare and contrast asexual and sexual reproduction.
FIGURE 1.1
One parent or two?
That is the main difference between sexual and asexual reproduction. Sexual reproduction just means combining
genetic 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. For
many single-celled organisms, reproduction is a similar process. The parent cell simply divides to form two daughter
cells that are identical to the parent. In many other organisms, two parents are involved, and the offspring are not
identical to the parents. In fact, each offspring is unique. Look at the family in Figure 1.2. The children resemble
their parents, but they are not identical to them. Instead, each has a unique combination of characteristics inherited
from both parents.
Reproduction is the process by which organisms give rise to offspring. It is one of the defining characteristics of
living things. There are two basic types of reproduction: asexual reproduction and sexual reproduction.
Asexual Reproduction
Asexual reproduction involves a single parent. It results in offspring that are genetically identical to each other
and to the parent. All prokaryotes and some eukaryotes reproduce this way. There are several different methods of
asexual 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.
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FIGURE 1.2
Family Portrait: Mother, Daughter, Father,
and Son. Children resemble their parents,
but they are never identical to them. Do
you know why this is the case?
• 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 from
a 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 while
it grows and develops. When the bud is fully developed, it breaks away from the parent cell and forms a new
organism. Budding in yeast is shown in Figure 1.3.
FIGURE 1.3
Starfish reproduce by fragmentation and yeasts reproduce by budding. Both are types of asexual reproduction.
Asexual reproduction can be very rapid. This is an advantage for many organisms. It allows them to crowd out
other organisms that reproduce more slowly. Bacteria, for example, may divide several times per hour. Under ideal
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Chapter 1. Lesson 1: Asexual vs. Sexual Reproduction
conditions, 100 bacteria can divide to produce millions of bacterial cells in just a few hours! However, most bacteria
do 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 of
most other organisms as well.
Sexual Reproduction
Sexual reproduction involves two parents. As you can see from Figure 1.4, in sexual reproduction, parents produce
reproductive cells—called gametes—that unite to form an offspring. Gametes are haploid cells. This means they
contain only half the number of chromosomes found in other cells of the organism. Gametes are produced by a
type of cell division called meiosis, which is described in detail in a subsequent concept. The process in which two
gametes unite is called fertilization. The fertilized cell that results is referred to as a zygote. A zygote is diploid
cell, which means that it has twice the number of chromosomes as a gamete.
Mitosis, Meiosis and Sexual Reproduction is discussed at http://www.youtube.com/user/khanacademy#p/c/7A96
46BC5110CF64/7/kaSIjIzAtYA .
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/275
FIGURE 1.4
Cycle of Sexual Reproduction.
Sexual
reproduction involves the production of
haploid gametes by meiosis. This is followed by fertilization and the formation of
a diploid zygote. The number of chromosomes in a gamete is represented by the
letter n. Why does the zygote have 2n, or
twice as many, chromosomes?
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Summary
• Asexual reproduction involves one parent and produces offspring that are genetically identical to each other
and to the parent.
• Sexual reproduction involves two parents and produces offspring that are genetically unique.
• During sexual reproduction, two haploid gametes join in the process of fertilization to produce a diploid
zygote.
• Meiosis is the type of cell division that produces gametes.
Practice
Use this resource to answer the questions that follow.
• http://www.hippocampus.org/Biology → Biology for AP* → Search: Life Cycles
1.
2.
3.
4.
5.
6.
7.
8.
Define parthenogenesis.
What type of organisms can benefit from asexual reproduction?
What are the four major types of asexual reproduction?
Give two examples of organisms that reproduce by binary fission.
What is the difference between budding and fragmentation?
What is sexual reproduction?
How many chromosomes are in a human gamete?
What is meiosis?
Review
1. What are three types of asexual reproduction?
2. Define gamete and zygote. What number of chromosomes does each have?
3. What happens during fertilization?
4. Compare and contrast asexual and sexual reproduction.
References
1. Image copyright Juan Carlos Tinjaca, 2010. . Used under license from Shutterstock.com
2. Starfish image copyright asharkyu, 2010; yeast image copyright Knorre, 2010. . Used under licenses from
Shutterstock.com
3. CK-12 Foundation. . CC-BY-NC-SA 3.0
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