When the DNA molecule in the cell replicates, several chemical changes occur during this process. These changes are sometimes able to repair but there are some changes which cannot be changed. They are called as mutations. Due to the mutations DNA molecule cannot repair itself and passes to the next generation. Mutations have the ability that they can change the entire amino acid sequences of proteins which are present inside the gene. There are some mutations which do not affect the function of the proteins but some mutations are harmful that is they do not allow the amino acids to code properly for the protein and as a result the genes do not function properly.
How Do Mutations occur?
The changes in the DNA molecule can occur for following reasons:
1) In some cases, mutations are inherited that is they pass from parents to offspring.
2) Sometimes environmental changes affect the replication of DNA. Due to this, the DNA molecule cannot replicate properly. These mutations are acquired. In this kind of mutations, DNA molecule divides even before the cell division starts.
Types of Mutations:-
Point mutations occur when a single nucleotide is replaced with another nucleotide base. Insertion and deletion come in this category. Error in the process of replication of DNA molecule results in point mutations. Sometimes heat or high level radiations cause the error in DNA replication. There are different effects of point mutations. If this type of mutation occurs in the sequence of DNA molecule or exon, then the protein sequence changes present in that gene. If the mutation occurs in the intron region which is also the non coding region of the DNA molecule, then changes occur in the RNA effecting the coding of gene. Sickle cell anemia is caused by the point mutations. Changes occur in the beta hemoglobin. It converts GAG sequence into GUG. Point mutations can be subdivided into three types:
1) Nonsense mutations are the ones which code for the same amino acid.
2) Missense mutations occur in the genes which code for different amino acid.
3) Silent mutations do not affect the function of the proteins and code for different or same amino acid.
Mispairing of the DNA molecule causes the frameshift mutations. The changes in the single base pair nucleotide sequence usually insertion or deletion result in these mutations. The whole information coded in the amino acid changes due to frameshift mutations. As the gene's structure consists of three codons that is why if changes occur in these codons, the whole information present in that gene will change.
As the name shows, the mutations which occur in chromosomes are called as chromosomal mutations. These mutations occur when the chromosome undergo crossing over during the process of meiosis. Due to this type of mutation, many parts of the DNA molecule get affected and abortion takes place if any genetic disease occurs in the baby. There are different types of chromosomal mutations:
In this type, a piece of chromosome attaches to its non homologous part during crossing over. Translocation mutation can change the gene by breaking its real structure. Due to this the whole function of the gene changes. The disease of Leukemia occurs due to translocations between the chromosome 9 and 22. This hybrid gene creates a protein whose function is abnormal. Due to this abnormal gene, the normal growth of the cells stop and it ends up causing leukemia.
If some region of DNA molecule changes its position on a chromosome, then inversions occur.
Deletions cause the removal of a large part of the chromosome. Due to this, many genes are removed and the genetic material becomes mutated.
When the genes appear more than once on the same chromosome, they result in duplications.
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