In this explainer, we will learn how to describe the defining features of asexual reproduction and give examples of methods of asexual reproduction.
Reproduction is an incredibly important life process. It is the method by which an organism produces offspring. If all organisms stop reproducing, it will not be long until all the species start to die out at an alarming rate.
Reproduction is a biological process by which new offspring are produced from their parent(s).
There are two major types of reproduction: sexual and asexual. In this explainer, we will be focusing on the methods of asexual reproduction used by organisms to ensure the continued survival of their species.
Sexual reproduction is the method of reproduction used by humans. It involves two parent organisms combining their sex cells (gametes), in a process called fertilization, to produce new, genetically unique offspring. A simple outline of this is shown below in Figure 1.
Producing offspring by sexual reproduction helps increase the genetic variation of a population. Genetic variation describes the differences in the genetic material between individuals within a population. Generally, it is beneficial for individuals within the same population to be different from each other. This is because if any significant changes occurred in their environment, there are likely to be at least a few individuals who are well adapted to cope with such changes.
Key Term: Genetic Variation
Genetic variation describes the differences in the genetic material between individuals within a population.
Unlike sexual reproduction, asexual reproduction involves only one parent. There are various methods of asexual reproduction, but they all result in offspring that are pretty much genetically identical to the parent. You may sometimes see them referred to as clones of their parent. This means that, compared to sexual reproduction, asexual reproduction does not introduce much genetic variation into the population.
Key Term: Asexual Reproduction
Asexual reproduction is the process by which new offspring are produced from one parent only.
In asexual reproduction, because the parent does not have to spend time finding a mate and then spend time going through the process of fertilization, this process is generally much faster than sexual reproduction. This means that offspring can be produced very quickly.
Example 1: Recalling the Defining Features of Asexual Reproduction
Complete the following sentence: Asexual reproduction produces offspring that are identical to the parents, so it reduces genetic .
- not, expression
- genetically, variation
- almost, mutations
- partially, similarities
Reproduction is an incredibly important process for organisms. Successful reproduction allows organisms to make sure that their species continues to survive.
Asexual reproduction is the process by which a single organism produces offspring. Unlike sexual reproduction, it does not need two members of opposite sexes to mate to produce new offspring.
This benefits the organism in some ways, as this means that the organism does not have to spend valuable time and energy finding a mate. However, when a single organism produces offspring, the offspring are genetically identical to the parent; we may call this a clone.
If the parent organisms are genetically identical to their offspring in a population, we say that the genetic variation is low. This is because, by making clones of themselves, they have not introduced any different genes into their offspring that they did not have.
So, using this information and looking back at our answer options, we can see that the correct words to complete the sentence are as follows. Asexual reproduction produces offspring that are genetically identical to the parents, so it reduces genetic variation.
Now, let’s take a look at some examples of asexual reproduction in different organisms.
Bacteria are single-celled organisms. They are referred to as prokaryotic, which means that their genetic material is not contained within a special cellular structure called a nucleus but instead is freely floating within the cell. A simple drawing of a bacterium is shown in Figure 2.
When bacteria reproduce, they do so asexually using a process called binary fission. During this process, the parent cell splits into two separate daughter (offspring) cells, which are genetically identical to the parent cell. A basic outline of binary fission is shown in Figure 3.
Key Term: Binary Fission
Binary fission is a type of asexual reproduction in which a cell divides into two identical daughter cells.
In Figure 7, you can see that, before splitting, the bacterium replicates its genetic material. You may recall that this is very similar to the process of cell division used by eukaryotic organisms (those with cells that do have a nucleus), which is called mitosis.
Binary fission is also used by eukaryotic unicellular organisms, such as Amoeba, Paramecium, and Euglena.
Example 2: Recalling the Method of Asexual Reproduction Used by Bacteria
Salmonella bacteria are responsible for causing food poisoning in humans. The bacteria reproduce when a single bacterium divides into two. This happens repeatedly and rapidly in the right conditions. Which method of asexual reproduction is used by Salmonella?
- Vegetative propagation
- Binary fission
Bacteria are single-celled organisms that can be found in many different environments, including your digestive system. When a single bacterium reproduces, it replicates its genetic material before dividing into two. These two cells produced are its offspring and are referred to as daughter cells.
This type of reproduction is called binary fission. The part bi- means “two” and refers to the two daughter cells that are produced. Under the right conditions, Salmonella can go through this process once every 40 minutes. This means if you started with a single bacterium, after 24 hours, you will end up with 68 billion bacteria.
So, we can conclude that the method of asexual reproduction used by Salmonella is binary fission.
Fungi are a large group of organisms that are classified as eukaryotes because they possess a nucleus. Fungi show some interesting examples of asexual reproduction.
Yeast are single-celled fungi. You may know that a species of yeast commonly called baker’s yeast is used to help bread rise. Yeast cells can reproduce asexually using a process called budding. A brief outline of budding in yeast cells is shown in Figure 4.
Key Term: Budding
Budding is a type of asexual reproduction in which a new organism develops from a bulge or bud attached to the parent organism.
You may also be able to see the process of budding for yourself. The following is a simple experiment to view budding in yeast cells.
Demonstration: Viewing the Process of Budding in Yeast Cells
You will need a sample of yeast, a sugar solution, some warm water, and a microscope with slides and coverslips.
Step 1: Make a yeast solution by combining a small sample of yeast with 100 mL of warm water and a tablespoon of sugar.
Step 2: Leave the solution for a couple of hours, or longer if needed.
Step 3: Take a small amount of the mixture and place it on a glass slide.
Step 4: Gently place a coverslip on the glass slide.
Step 5: Look through the microscope’s eyepiece at the lowest magnification; if you need, adjust the height of the stage to bring the image into focus.
Step 6: Once you have the image in focus, switch to a higher magnification. If the yeast is budding, you may be able to see something like the cell at the bottom of the cluster in the image below.
Budding can also be used by other organisms, such as aquatic sponges or small freshwater Hydra, like the one with a lateral bud shown in the picture below. In all of these organisms, the process of budding involves a small growth on the parent eventually detaching and developing into a new organism, which is genetically identical to the parent.
Example 3: Describing the Process of Budding in Hydra
The flowchart outlines the stages of budding, an asexual process used by Hydra.
Which of the following correctly completes the flowchart?
- The bud splits into two new Hydra organisms.
- The bud develops into a small individual that detaches from the parent.
- The bud attracts another Hydra to mate with the original parent.
There are many different types of asexual reproduction that can be used by organisms. One type is budding, which is a process used by yeast, fungi, and Hydra, as mentioned in the question. Hydra are small freshwater organisms that are considered very interesting to scientists as they do not appear to grow old.
During the process of budding, the parent cell or organism produces a bud or growth. The parent cell or organism then replicates its DNA so that the bud contains exactly the same genetic material as that of the parent.
When the conditions are right, the bud continues to grow. When it is ready, it detaches from its parent, and a completely new organism is produced, which is genetically identical to the parent.
Let’s use this information and take a look back at our answer options.
During the process of budding, the bud itself does not split into more than one organism. It simply grows and then detaches from the parent when ready. Budding is an asexual process, which means only one parent organism is involved. This means that at no point will the bud attract another Hydra to mate with the parent Hydra.
Therefore, the correct statement to complete the flowchart is that the bud develops into a small individual that detaches from the parent.
Other species of fungi, such as the one that causes bread mold and the giant puffball mushroom, can use special structures called spores to reproduce asexually.
Key Term: Spores
Spores are special reproductive cells that contain half the genetic material contained in the cells of the parent organism. Spores can be used in asexual and sexual reproduction.
Spores are cells that contain only half of the genetic material of the cells of the parent fungi, and so they are referred to as haploid. The parent organism produces spores and stores a huge number of them in a sac called a sporangium. When ready, the sporangium bursts and releases these spores.
When these spores find a suitable environment to grow, they can develop into new individuals without ever being fertilized.
Asexual reproduction in the animal kingdom is rare, but there are some interesting examples.
Regeneration is an asexual process used by organisms like starfish (sea stars) and flatworms. Regeneration can be used by these organisms to regrow removed limbs or even to produce an entirely new organism.
Key Term: Regeneration
Regeneration is the ability of an organism to regrow damaged or missing parts and is sometimes used as a type of asexual reproduction.
For example, a starfish (pictured below) may lose one of its arms as a result of predation or injury. As long as the central disk is intact, it can regrow this lost arm.
Although this is an example of regeneration, it is not strictly an example of reproduction, as it does not involve the production of a new organism. Let’s take a look at an example of regeneration that results in the production of a completely new organism.
If a flatworm was cut into pieces, it would be able to regenerate new cells. These cells would grow and specialize, eventually replacing the part of the flatworm that was originally removed. So, if a single flatworm was cut into two pieces, it would regenerate to form two flatworms. Figure 7 below shows a simple outline of this process.
Example 4: Identifying the Different Methods of Asexual Reproduction
The table below outlines some asexual reproductive methods and the organisms that use them.
|Salmonella bacteria||Binary fission||The parent cell doubles its genetic material, |
before splitting into two separate cells.
|Yeast||Budding||The parent cell forms a “growth” that grows into |
a small individual and eventually detaches from
the parent cell.
|Flatworm||X||The parent worm splits into two parts, and each of |
these parts grows into a new organism.
What should replace X?
- Vegetative propagation
Asexual reproduction is a type of reproduction that produces genetically identical offspring from a single parent. This method of reproduction is common in microorganisms like bacteria and can even be used by some members of the animal kingdom.
Flatworms (scientific name: Platyhelminthes) are members of the animal kingdom that can use asexual reproduction to produce offspring from a single parent organism. If a flatworm is split into parts, or perhaps loses a section of its body, it can regenerate the missing sections. This is outlined in the diagram below.
The process of growing back those missing parts by flatworms is called regeneration. When we talk about something being regenerated, we mean that something has been renewed or restored. This is exactly what is happening here; the flatworm is restoring parts of its body that have been lost.
Therefore, X in the table should be replaced by regeneration.
Plants can also make use of asexual reproduction to rapidly produce new, genetically identical offspring.
The method of asexual reproduction that plants commonly use is vegetative propagation. Using this method, plants can produce new organisms from growths on their leaves, stems, and roots.
Key Term: Vegetative Propagation
Vegetative propagation is a type of asexual reproduction in which a new plant grows from part of the parent plant.
An example of a plant that uses vegetative propagation is the strawberry plant. This plant extends its roots through the ground, and new plants sprout up from its roots. Figure 8 shows a simple outline of this method of reproduction.
Vegetative propagation can provide lots of benefits. For humans, this means we can grow lots of desirable crops. For plants, this means that they can quickly produce a large population. However, because all forms of asexual reproduction produce clones of the parent organism, vegetative propagation does not introduce any new genetic variation into the population. This puts the species at risk of not being able to adapt to new conditions in the environment.
Let’s summarize what we have learned about asexual reproduction in this explainer.
- Asexual reproduction requires only one parent organism, and this process produces clones of the parent organism.
- Asexual reproduction does not introduce much genetic variation into the population.
- The methods of asexual reproduction include
- binary fission (bacteria),
- budding (yeast, hydra, and sponges),
- production of spores (fungi),
- regeneration (starfish, Planaria),
- vegetative propagation (plants).