Aneuploidy & Polyploidy: Definition & Examples

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  • 0:00 Definition of Ploidy
  • 1:04 Definition of Aneuploidy
  • 2:26 Examples of Aneuploidy
  • 3:08 Definition of Polyploidy
  • 3:55 Examples of Polyploidy
  • 4:55 Lesson Summary
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Lesson Transcript
Instructor: Adrianne Baron

Adrianne has a master's degree in cancer biology and has taught high school and college biology.

We are going to cover the terms ploidy, aneuploidy, and polyploidy in this lesson. We'll also explain how each of these occurs and get examples of each.

Definition of Ploidy

Every feature of our bodies - from eye color to hair color to height and the shape of your ears - are all determined by the genes located on our chromosomes. Genes are the instructions for building our bodies, and chromosomes are the structures that carry genes. Our bodies are so intricate that it takes many, many genes on several chromosomes in order to construct all our features.

As a matter of fact, there are 2 sets of 23 chromosomes that give the instructions for our bodies. These numbers represent what is known as our ploidy number, which is the number of sets of chromosomes a species has. As humans, we are considered to be diploid since we have 2 sets of chromosomes. You can remember this easily by recalling that the prefix di- means 2. Diploid is often abbreviated as 2n. There are many other animals that are also diploid. Most mammals, such as dogs, cats, whales, and dolphins, are diploid.

Definition of Aneuploidy

There are exceptions to this, just like there is with everything in life. We have to keep in mind that each set of chromosomes comes from the parents that produced us. The egg and sperm cells that they used to produce us should therefore each contain 23 chromosomes in them. This is referred to as haploid, since there is only one set of chromosomes and that is half of the full number. This is abbreviated as n. When the egg and sperm join, then this will give the 2 sets of 23 chromosomes, resulting in 46 chromosomes.

However, it is possible for our bodies to produce sperm and eggs that don't contain the normal number of chromosomes. In some instances, there may be an extra chromosome or a missing chromosome. When an egg or sperm with an abnormal number of chromosomes is joined with a normal egg or sperm, then the resulting fertilized cell will not have 46 chromosomes. This is referred to as aneuploidy.

We most commonly see this resulting in a person with 45 or 47 chromosomes. Since there is a change in the number of chromosomes, then these individuals are no longer considered to be diploid, or 2n. If there is only 1 less chromosome, then they are monosomic, abbreviated as 2n - 1. If there is 1 extra chromosome, then they are trisomic, abbreviated as 2n + 1.

Examples of Aneuploidy

You are likely familiar with one example of aneuploidy. Down Syndrome is a disorder that results from an extra copy of 1 chromosome. The most common cause of Down Syndrome is an extra copy of chromosome 21. This is why you will sometimes hear people referring to this disorder as trisomy 21.

There may also be changes in the number of chromosomes that determine what sex we are. A very common disorder resulting from an extra Y chromosome is Klinefelter Syndrome. This happens when a sperm cell contains 2 Y chromosomes and then joins with an egg cell that has the normal 1 X chromosome. The individual with an extra Y chromosome is still male, but they are usually bigger than the average male.

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