Copyright

What is Aneuploidy?

Adrianne Baron, Darla Reed
  • Author
    Adrianne Baron

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

  • Instructor
    Darla Reed

    Darla has taught undergraduate Enzyme Kinetics and has a doctorate in Basic Medical Science

Learn the definition of aneuploidy. Understand the different conditions of aneuploidy. Learn about aneuploidy disorders and the diagnosis of aneuploidy. Updated: 10/20/2021

Table of Contents

Show

What is Aneuploidy?

There are normally two copies of each chromosome, or long piece of DNA, in each cell. In abnormal instances there may be more or less than two copies of each chromosome in the cell. This is referred to as aneuploidy. Aneuploidy occurs when there are errors during the process of meiosis. This is the process to create sex cells in the body. Normally, each sex cell should have one copy of each chromosome.

1 copy of each chromosome in daughter cells in meiosis

Diagram of meiosis

In aneuploidy, however, there are either 2 chromosomes where there should be one or the chromosome is missing altogether. During meiosis, one parent cell divides into two daughter sex cells. Each daughter sex cell should get one of each chromosome from the parent cell as the cell divides into two.

Aneugens

What? causes these errors in meiosis to occur that lead to aneuploidy? Some are caused by substances known as aneugens. Aneugens are agents that are capable of interfering with the normal function of cell division by causing the spindle fibers to not separate chromosomes properly. Some of the most common aneugens are pesticides, tobacco smoke, perfluorinated carbons, benzene and insecticides. X-rays are also a known aneugen. Aneugens are also referred to as genotoxicants.

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Gametogenesis: Definition & Concept

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
 Replay
Your next lesson will play in 10 seconds
  • 0:05 What Is Aneuploidy?
  • 1:38 How Does Aneuploidy Happen?
  • 3:20 Monosomy Disorders
  • 3:40 Trisomy Disorders
  • 4:52 Trisomy in Sex Chromosomes
  • 6:31 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Timeline
Autoplay
Autoplay
Speed Speed

Different Conditions of Aneuploidy

In normal body cells where there are two copies of each chromosome, it is notated as 2n where n refers to the chromosome. This notation comes from the fact that when two sex cells come together, they each bring their one copy of each chromosome into the new body cell. This gives two copies of each chromosome in every body cell. The total number of chromosomes should be 46. The notation is different in the different conditions of aneuploidy because they do not have exactly two copies of each chromosome.

Nullisomy

The first aneuploidy condition is nullisomy. Nullisomy is when a pair of chromosomes is missing. This occurs due to what is known as nondisjunction during the process of meiosis. Nondisjunction is when both of the chromosomes that should separate and end up in different daughter sex cells both end up in one daughter sex cell. This leaves the other daughter sex cell without a copy of the chromosome at all. When two sex cells without the chromosome are joined together during fertilization then the chromosome pair is missing and this is known as nullisomy. Nullisomy is notated as 2n -2. meaning there are two copies of the chromosome that are missing in the body cell. This would cause the total number of chromosomes in the cell to be 44. This particular aneuploidy is fatal and does not produce a viable baby.

Monosomy

Monosomy is when one chromosome is missing from the set of chromosomes. Instead of there being two copies of the chromosome, there is just one copy of the chromosome. This occurs when one sex cell without one copy of one chromosome joins during fertilization with another sex cell that has the normal one copy of each chromosome. The resulting number of chromosomes in the body cell will be 45 instead of the normal 46. This condition can produce a viable baby depending on which chromosome is missing. The notation for this condition is 2n-1 indicating that there are two copies of each chromosome minus 1 chromosome.

Trisomy

The next aneuploidy is trisomy which is when there is one extra copy of one of the chromosomes. This occurs because of two sex cells coming together during fertilization where one sex cell has an abnormal two copies of a chromosome and the other sex cell has one copy of the chromosome. This results in the body cell having three copies of the chromosome rather than the normal two copies. The total number of chromosomes in this cell will be 47 instead of the normal 46. The notation for this condition is 2n + 1 meaning there are two copies of each chromosome plus an additional chromosome. This condition can produce a viable baby depending on which chromosome is affected.

Tetrasomy

Tetrasomy is the last of the aneuploidies. In the case of tetrasomy, a body cell has four copies of one of the chromosomes. This occurs when two sex cells that each have two copies of the chromosome come together during fertilization. Since each sex cell has two copies, this gives the body cell four copies rather than the normal two. The total number of chromosomes in the body cell ends up being 48 instead of the normal 46. The notation for this condition is 2n + 2 meaning there are two copies of each chromosome plus 2 additional chromosomes. This condition can result in a viable baby depending on which chromosomes are involved. The most common chromosomes involved in this condition are the sex chromosomes.

Aneuploidy Disorders

There are several different aneuploidy disorders of most of the different conditions of aneuploidy. As mentioned earlier, nullisomy is fatal and doesn't produce a viable baby so there are no nullisomy disorders.

To unlock this lesson you must be a Study.com Member.
Create your account

Frequently Asked Questions

What are the four types of aneuploidy?

The four types of aneuploidy are nullisomy, where both copies of a chromosome are missing, monosomy, where one copy of a chromosome is missing, trisomy, where there is one extra chromosome, and tetrasomy, where there is an extra set of one of the chromosomes.

What are examples of aneuploidy?

Some examples of aneuploidies include Trisomy 21 also called Down Syndrome, Klinefelter's Syndrome, cri du chat syndrome also called cat cry syndrome, Turner Syndrome, Trisomy 18 also called Edward's Syndrome, Tetrasomy X,

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days