Chromosomal or structural mutation
It changes the nucleotide sequence in DNA and therefore also the message transcribed to the mRNA . More or less large segments of the chromosomes are affected, causing changes in their structure , affecting several genes .
Types of chromosomal mutations:
- If they affect the order of genes:
- If they affect the number of genes:
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Alterations in the order of genes
Two types are distinguished:
It consists in that a chromosomal fragment has rotated 180º, so its gene sequence is inverted with respect to that of the rest of the chromosome.
As a result of inversions, loops can form during meiosis , rendering the gametes nonviable.
There are two types of inversions according to their relationship with the centromere:
- Pericentric: They affect the centromere, and produce a change in the shape of the chromosome.
- Paracentric: The centromere is not affected or the shape of the chromosome.
Example: hemophilia A, due to inversion affecting the factor VIII gene , on the X chromosome.
Video: Chromosome Inversions.
Video: Investment paracéntica I.
It consists of the change of position of a fragment of the chromosome.
The translocation can occur on the same chromosome, on homologous or different chromosomes.
The mutation can be reciprocal , if fragments are exchanged, or not reciprocal, and is called transposition.
An example: chronic myeloid leukemia, by reciprocal translocation between fragments of chromosomes 9 and 22.
Alterations due to the existence of an incorrect number of genes
They are produced as a consequence of an error in the meiotic pairing that can produce an erroneous crossover, leaving one chromosome with one more fragment and the other with one less fragment. They can also be the consequence of investments or translocations of the parents.
The gametes produced, after fertilization, could cause:
The deletion is produced by the loss of a chromosomal fragment, and therefore, of the genes it contains. They are usually fatal in homozygous individuals.
An example of a deletion in humans on chromosome 5 is the one that produces the cat's meow syndrome , due to the characteristic cry of babies who suffer from it.
Video: Cat Meow Syndrome .
Duplication occurs when a chromosomal fragment is repeated on the same or another chromosome.
Consequences of chromosomal mutations
The translocations and investments, to not changing the number of genes, usually not greatly affect the carrier. The problem is greater when a gene ends up further away from other areas of the chromosome that control its expression or when they approach other regulatory areas that do not correspond to it.
Types of chromosomal or structural mutations:
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