Deletion Mutation: Definition, Examples & Diseases

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  • 0:00 Deletion Mutation and DNA
  • 2:25 Examples of Deletion
  • 3:50 Diseases
  • 6:01 Lesson Summary
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Lesson Transcript
Instructor: Nicholas Gauthier
Mutations are errors in the replication of DNA. Sometimes a piece of DNA can be deleted from the copy, creating a devastating effect on the organism's ability to manufacture an important protein. This can lead to disease.

Deletion Mutation and DNA

A deletion mutation occurs when part of a DNA molecule is not copied during DNA replication. This uncopied part can be as small as a single nucleotide or as much as an entire chromosome. The loss of this DNA during replication can lead to a genetic disease.

Nucleotides are subunits of DNA, and each nucleotide is made of a sugar molecule called deoxyribose, a phosphate group, and a nitrogenous base. There are four different nitrogenous bases in DNA, and they are represented by the letters A, C, G, and T. The complete nucleotides (deoxyribose, phosphate, and nitrogenous base) are named adenine, cytosine, guanine, and thymine. Every DNA sequence is a long chain of these four nucleotides.

Nucleotides

Each DNA molecule has two strands, a master strand and a complementary strand. The strands each have the same types of nucleotides. Where an A exists on the master strand and a T is present on the complementary strand, and vice versa. Where a G is present on the master strand, there is a corresponding C on the complementary strand, also vice versa. Such a bonding of A to T or G to C is called a base pair. In this image, note how there are two strands and that nucleotides bond with those on the opposite strand. The S stands for sugar, and the P stands for phosphate.

DNA

Every three nucleotides in certain sections of DNA make up a codon. For example, if a DNA segment reads AGT-CGT, then it is made of two codons: AGT and CGT. What's more, each codon corresponds to a specific amino acid. These amino acids are the subunits that make up proteins. Therefore, the sequence of codons in DNA determines the sequence of amino acids in proteins.

So, for example, AGT codes for the amino acid serine, while CGT codes for the amino acid arginine. Therefore, AGT-CGT calls for serine and arginine to be joined together in a protein.

Examples of Deletion

In a point mutation, an error occurs in a single nucleotide. The entire base pair may be missing, or just the nitrogenous base on the master strand. For point deletions, one nucleotide has been deleted from the sequence. For example, if the original sequence is ATG-AGT-CGT-ATA-TAA, it will code for methionine, serine, arginine, isoleucine, and finally the STOP codon (telling the cell to stop protein production).

After a point deletion, the new sequence might be ATG-AGC-GTA-TAT-AA. In this case, a T has been deleted. The new amino acid sequence is methionine, serine, valine, tyrosine, and then the final AA doesn't code for anything.

While some amino acids may be the same, the deletion creates a frame shift, causing changes down the line.

Frame Shift

A chromosome deletion is also possible, where an entire section of a chromosome is deleted. This can involve any number of base pairs as long as it is more than one (that would be a point deletion). Sometimes an entire chromosome can be deleted as well. Whenever any DNA is deleted during replication, any number of genetic diseases can occur.

Segment Deletion

Diseases

22q11.2 deletion syndrome is caused by the deletion of a small section of chromosome 22. It results in a cleft palate, heart defects, autoimmune disorders, and more. The symptoms vary wildly and can be accompanied by learning disabilities and mental illness.

Cystic fibrosis is caused by a point deletion. The deletion affects the protein that moves water and salt in and out of cells. It tends to result in mucus building up in different parts of the body. The respiratory and digestive systems are usually the most affected. Many people with cystic fibrosis die in their 30s.

Infections are common, particularly in the respiratory system. Cysts tend to occur in the pancreas. Small body size and infertility are also possible.

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