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Chromosome Structure Changes
Next Generation: HS.LS3.2 HS.LS3.2

Chromosome Structure Changes

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This lesson will identify how the structure of a chromosome can change and the implications that come from changes in chromosomes.

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Tutorial

What's Covered

This lesson is going to cover changes in chromosome structure by examining:

  1. Gene Mutation
  2. Karyotypes

1. Gene Mutations

A gene mutation is the change in the nucleotides that make up a gene. Sometimes, chromosome structure can be altered during cell division, which will lead to a certain type of gene mutation. These gene mutations can include:

  • Deletions
  • Translocations
  • Duplications

A deletion is the removal of one or more genes on the chromosome.

ExampleCri-du-chat is a disorder that is caused by a deletion on chromosome number five. With this type of disorder, a baby's larynx will not properly develop, so that when the baby cries, it will sound like a meowing cat. This disorder can also be associated with abnormal mental development as well.

Term to Know

    • Deletion
    • When part of a chromosome is deleted; sometimes it may not have any effect while other times it does.
    • Cri-du-chat
    • A genetic disorder caused by the deletion of a section of the 5th chromosome; cri-du-chat is French for “cry of the cat”. Cri-du-chat causes physical and cognitive abnormalities.

Translocation is when part of one chromosome switches place with a corresponding part of another nonhomologous chromosome. This type of gene mutation can lead to certain types of cancers.

ExampleSay an original chromosome is made of A, B, C, D, E, F, and a nonhomologous chromosome contains G, H, I, J, K, L. In a translocation, part of one chromosome will switch places with a corresponding part of the nonhomologous chromosome. In this case, the F and L parts of the chromosome could switch places.

Term to Know

    • Translocation
    • A chromosome abnormality that occurs when nonhomologous parts rearrange and fuse together.

Duplication is when a nucleotide sequence is repeated. Duplications are generally not harmful, and they actually have not been linked to any particular genetic disorder, unlike deletions and translocations.

Example Say a chromosome is composed of A, B, C, D, E, F. If a duplication occurs, it might end up with A, B, C, B, C, D, E, F, with the B, C portion repeated.

Term to Know

    • Duplication
    • Sequences of nucleotides are repeated multiple times, they haven’t been linked to disorders, but have been linked to cancers.

2.Karyotypes

Karyotypes are the arrangement of a person's complete set of chromosomes by length, shape, and the location of the centromere. These pictures are taken well in metaphase of mitosis, because the chromosomes at that point are most easy to identify. The chromosomes will be photographed through the microscope, cut out, and arranged from the largest all the way down to the smallest. The last pair of chromosomes in a karyotype are always the sex chromosomes.

Term to Know

    • Karyotype
    • Looking at the number of chromosomes and their characteristics under a microscope, this is a critical tool in assessing genetic disorders in a developing embryo.

Chromosomes.png

These karyotypes allow you to see a picture of a person's chromosome. This can help to identify any abnormalities. We can tell by looking at the above karyotype that this person is a male because the 23rd pair of chromosomes are different. One is an X chromosome, and one is the Y chromosome. One abnormality that can be seen on a karyotype is Trisomy 21, a genetic disorder in which a person has three copies of chromosome number 21. Here is an example of what this might look like:

downs.png

If the orange line were a third chromosome in the 21st pair, then the person would have trisomy 21; also known as Down Syndrome.

Summary

Gene mutations are changes in the nucleotides that make up a gene. These mutations can include deletion, translocations, and duplications. A deletion is the removal of one or more genes on the chromosome. Translocation is when part of a chromosome switches place with the same part of a nonhomologous chromosome. Duplication occur when part of a chromosome becomes repeated; this mutation is not linked with any genetic disorder. A karyotype is looking at a person's chromosomes under microscope to check for genetic abnormalities. This can identify if someone has Down Syndrome.

Keep up the learning and have a great day!



Source: SOURCE: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND

TERMS TO KNOW
  • Karyotype

    Looking at the number of chromosomes and their characteristics under a microscope, this is a critical tool in assessing genetic disorders in a developing embryo.

  • Duplication

    Sequences of nucleotides are repeated multiple times, they haven’t been linked to disorders, but have been linked to cancers.

  • Translocation

    A chromosome abnormality that occurs when nonhomologous parts rearrange and fuse together.

  • Cri-du-chat

    A genetic disorder caused by the deletion of a section of the 5th chromosome; cri-du-chat is French for “cry of the cat”. Cri-du-chat causes physical and cognitive abnormalities.

  • Deletion

    When part of a chromosome is deleted; sometimes it may not have any effect while other times it does.