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Chromosomal Rearrangement

Chromosomal Rearrangement
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  • 0:01 Chromosomal Rearrangements
  • 0:30 Deletions & Duplications
  • 2:50 Inversions & Translocations
  • 6:35 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
Have you ever switched out one thing for another or traded places with someone? Our chromosomes can do this, too. This lesson tells you how as we go over chromosomal rearrangements!

Chromosomal Rearrangements

Genetics can be boring. Unless, that is, we make it a participatory event. So assuming you have a pen and pencil or laptop next to you, let's play along together as we go over four different kinds of chromosomal rearrangements. These are chromosomal abnormalities where a chromosome's structure is reorganized through deletions, inversions, translocations, or duplications - all of which will be defined in due course.

Deletions & Duplications

Okay, using the laptop or pen and paper in front of you, let's type or write out the following: ABCDEFG. This whole string will represent a chromosome, with the individual letters representing genetic material within that chromosome.

Now go ahead and delete or cross out the D so that we're left with ABCEFG. That is, quite simply, a deletion, or a rearrangement that results in the removal of a segment of DNA, our genetic material. If the deletion occurs within a chromosome, like in our example, it's termed an interstitial deletion. If a deletion occurs at the end of a chromosome, we call this a terminal deletion. This would be like if we'd deleted the G in ABCDEFG instead of the D.

Okay. Now let's take that original whole chromosome of ABCDEFG and let's add in an additional BC right after the original BC to get ABCBCDEFG. What is this? This is a duplication, a rearrangement that results in an increase in the number of copies of a segment of chromosome. If the duplicated segments are located next to one another, as in our example, this is known as tandem duplication. This can occur in the same order, as in ABCBCDEFG, or in reverse order, as in ABCCBDEFG.

If the duplicated copy is found in a different region of the same chromosome or in another chromosome, we call this an insertional duplication. In our prior example, that would be like ABCDEFG turning into ABCDEFBCG, where the new BC is found in between F and G instead of right after the original BC.

Inversions & Transcolations

Okay. Let's get back to our original chromosome, ABCDEFG, and then let's tinker with it again. If you take ABCDEFG and flip BCD 180 degrees, what will you get? ADCBEFG. This is an example of an inversion, which is a rearrangement where a segment of chromosome is removed, rotated 180 degrees, and inserted into the same spot.

There are two types of inversions: paracentric and pericentric. To understand this, we need to rewrite ABCDEFG a little bit. Let's put a little dash in between ABC and DEFG, giving us ABC-DEFG. The dash in between ABC and DEFG represents the chromosome's centromere. The centromere is, quite simply, the part of the chromosome connecting chromatids together.

Now, if the inversion includes the centromere, we call this a pericentric inversion because 'peri-' means around or about. An example of this would be ABC-DEFG turning into AD-CBEFG. Note how the dash, representing the centromere, has moved because we inverted the segment BC-D 180 degrees into D-CB. If the inversion doesn't include the centromere, we call this a paracentric inversion because 'para-' means apart from or beyond. This would be like ABC-DEFG turning into ABC-DFEG, where the segment EF is reversed into FE.

And finally, let's rewrite everything back to our original ABCDEFG. Then, next to this, let's write in HIJKLM to represent a non-homologous chromosome. Non-homologous just means that it's a chromosome that's not of the same pair as the first one. This means we have:

  • ABCDEFG
  • HIJKLM

But what if we turn this into the following?

  • CDEFG
  • ABHIJKLM

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