Inversion Mutations: Causes & Effects

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  • 0:00 Chromosome Inversion
  • 0:52 Pericentric vs Paracentric
  • 2:13 Effects
  • 3:27 Lesson Summary
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Lesson Transcript
Lisa Roundy

Lisa has taught at all levels from kindergarten to college and has a master's degree in human relations.

Expert Contributor
Brenda Grewe

Brenda has 25 years of experience teaching college level introductory biology and genetics. She earned her PhD in Genetics from Indiana University.

Inversion mutations are one type of genetic mutation that creates changes in a chromosome. In this lesson, you'll learn about what causes an inversion mutation and the effects of the mutation.

Chromosome Inversion

Imagine you're typing the following sentence on your computer: 'The quick brown fox jumps over the lazy dog.' You know this is what you typed, but when you look at the screen it says: The quick brown spmuj xof over the lazy dog. Somehow, a glitch in the system reversed the order of the letters in the middle of the sentence, and now it's not clear what's happening over the lazy dog!

This example looks just like one type of mutation that can occur during the reproductive process. A mutation is any type of change in genetic material. An inversion mutation happens when a section of DNA breaks away and reattaches to the chromosome in a reversed order. This can be a small section of DNA that breaks away or a large section containing many different genes.

Pericentric vs Paracentric

There are two types of inversion mutations:

A paracentric inversion occurs when there is a break to only one arm of the chromosome, and the inverted segment does not include the centromere, or the area where the arms of the chromosome attach. For example, let's imagine the genes of a chromosome read ABCD-EFGH, where the hyphen is our centromere. If a paracentric inversion were to occur, the genes might now read ACBD-EFGH. Notice that the order of the C and B are reversed and that the inversion occurs on one side of the centromere.

A pericentric inversion is when the break occurs between two arms of a chromosome, and the inverted segment does include the centromere. Let's use our previous example of genes reading ABCD-EFGH, with the hyphen as our centromere. If a pericentric inversion were to occur, the genes might read ABCE-DFGH. Notice that this time the segment of D-E is reversed, which includes the centromere and moves genes from one arm of the chromosome to the other.

Of the two types of inversion mutations, a pericentric mutation is more likely to produce a genetic defect.


From our example, you can see how this could make the genetic code change or become more difficult to read. Sometimes when an inversion occurs, it also results in missing or extra copies of genetic material. When this happens, the genetic code can be so hard to decode that the resulting offspring will not survive or will have significant abnormalities.

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Additional Activities

Types and Effects of Inversion Mutations

As you have learned, inversions change the order of the genetic information for a particular chromosome. Depending on the location of the breaks in the DNA, the consequences of an inversion can vary from none to extremely serious. In the activity, you will explore the potential phenotypic effects of two hypothetical inversions in human chromosome 11.

The Activity

Human chromosome 11 is shown below. The cross-hatched region is the centromere. Numbers identify sections of the short (p) and long arms (q) of the chromosome, with each region containing multiple genes. The gene, HBB, for human beta globin (a subunit of hemoglobin) is located at p15.5, the white section at the left end of the chromosome. The CAT gene for the enzyme catalase also is located on the short arm at p11.13. A third gene, BEST1, which encodes Bestrophin-1 (a plasma membrane protein found in cells of the retina) is located on the long arm at q12.3.

U.S. National Library of Medicine

  1. Suppose that two breaks occur in one of the two copies of chromosome 11, one break at p14.1 and a second at q12.3. The region between the breaks is inverted when the breaks are repaired. Draw the rearranged chromosome 11. Does the inversion include the centromere? What type of inversion is this?
  2. Suppose that a break occurs in chromosome 11 at p15.5 and a second break occurs at p11.13 of the same homologue and the region between the breaks is inverted. Draw the rearranged chromosome 11. What type of inversion is this?
  3. Suppose that in the first inversion, the break in the q12.3 region splits the BEST1 gene into two parts, making it nonfunctional. Considering that most known mutations in the BEST1 gene are dominant, predict the phenotypic consequences for individuals with this inversion and one normal chromosome 11. To learn more about the function the BEST1 protein go to:
  4. Suppose that in the second inversion, the two breaks in the DNA occurred in the middle of the HBB gene and near the middle of the CAT gene, respectively. Considering that the majority of HBB and CAT gene mutations are recessive, predict the phenotypic consequences for individuals who have one inverted chromosome 11 and one normal chromosome 11. To learn more about the HBB and CAT gene functions go to: and

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