Earlier and still in some of the places marriages within close relations are very common. But have you ever wondered why should you not marry in close relations?
It’s because marriages in close relations lead to health issues for the child. They will end up having congenital problems. Some known such cases are children with heart problems, nervous disorders, organ malfunction, limb anomalies and many other genetic disorders.
We already know the fact that children inherit genetic information from his/her parents. So, the child inherits genes from its parents and when genes mutate then the chances of having a disorder in child increases.
Disorder depends on the type of gene mutation child is having. When you marry the relatives of the one who might have such gene mutation, then child inherits two copies of such mutated gene. So when someone marries outside the community, s/he brings in genes from the larger gene pool and the chances that child inherits the problem reduces remarkably.
What is mutation?
The two major processes that are responsible for genetic variation are mutation and recombination. A mutation is a significant inheritable alteration from the normal. It is the ultimate source of evolutionary change. The term mutation covers a broad array of different kinds of changes.
The mutational event that takes place within individual genes is called gene mutation. Whereas the mutational change that affects entire chromosome is known as chromosome mutation. Chromosome mutation covers all those cases that include deletion, addition or edition of a chromosome or a complete set of chromosomes. This leads to variation in number and size of the chromosomes.
Ultimately, it causes various syndromes in the organisms. We will discuss chromosomal variations in detail later on.
Now, let’s have brief information about gene mutation. Gene mutation is a change in the DNA sequence of a gene; ie., deletions, insertions or rearrangement of DNA sequence in the genome. New alleles do rise in all organisms, it may be spontaneous or due to radiation and chemicals in the environment. These new alleles will act as raw material for the second level of variation. Many kinds of gene alterations can occur within DNA molecules.
Geneticists classify mutation in a variety of ways.
- The basic classification in a multicellular organism is based on the type of cell in which the mutation first occurs- The mutation that arises in the cells that ultimately form gametes are ‘germ-line mutation’ and all other mutations line under ‘somatic mutation’. The mutations that occur in somatic cells are not transmitted to the next generation but may lead to altered cellular function or tumors.
- Mutations within genes located on the autosomes are called as ‘Autosomal mutations’. Likewise, the mutations within the genes located on X and Y chromosomes are respectively known as ‘X–linked mutation’ and ‘Y–linked mutation’.
- The simplest type of mutation is a base substitution, where a simple nucleotide pair in DNA is replaced with a different nucleotide pair. For instance, in A-G substitution, A is replaced with a G in one of the DNA strands. Some base substitutions replace one pyrimidine base with the other. They are called Transition mutations.
- T→C or C→T (pyrimidine→pyrimidine)
- A→G or G→A (purine→purine)
- Other base substitutions replace a pyrimidine with a purine or a purine with a pyrimidine. They are called Transversion mutations.
- T→A, T→G, C→A or C→G (pyrimidine→purine)
- A→T, A→C, G→T or G→C (purine→pyrimidine)
- The insertion or deletion of one or more nucleotides at any point within the gene leads to the change in all the subsequent three-letter codon. These are said to be Frameshift mutations, as the frame of triplet reading is altered during translation.
- Mutations are also classified according to several other schemes. Mutations can be called either spontaneous or induced based on their cause. Spontaneous mutation is an alteration in the nucleotide of a gene for which there is no known cause. It is not associated with an agent and considered to be accidental. Normally, biological and chemical processes in the organism that alter the structure of nitrogenous bases give rise to many of the spontaneous mutation. In contrast to this, the mutations that result from the influence of external factors are known to be induced mutations. The influence may be natural or even artificial agents. These agents are known as mutagens.
Now, you people got to know that mutation is a change in the DNA sequence of a gene. So, it’s clear that mutation is the ultimate reason for the phenotypic variation. Without the mutation, there would be no phenotypic variation, no adaptation to the changing environment, and no existence of evolution. This mutation gave rise to many hybrid plants yielding hybrid crops. We are in this era having hybrid fruits, veggies, flowers and hybrid cattle too. Also, we have so many advancements in health science based on mutation. So many advantages is that right!!!
Not really, everything has got its darker side too…
Yes, the mutation not only gives rise to new species but also leads to diseases and disorders. It is the basis for genetic diseases and cancers. Let’s know them in detail in our upcoming articles.