Evolution protects the living beings:
Resistance to disease is the key to maintain health and a balanced ecosystem. People with different physical capacities and backgrounds show the difference in their resistance power. All played by genetic diversity, only those who are fit can survive. Survival of the fittest is the key to life.
In addition to a healthy gene pool, the gene diversity exists in all the organisms including the plants, animals, and the human beings. Every entity on the earth has to respond to the changes in the environment. Not only the response is important, but also the adaptability to the changes occurring in the environment is quite substantial. Here evolution plays an important role. Evolution enables the species to improve its response to the environmental changes including the disease.
What is genetic diversity and variation?
The total number of different genetic characteristics is known as genetic diversity. Variable tendencies of genetic characteristics define genetic variability. Genetic variation is important for several reasons. It determines the potential for evolutionary changes. It also boosts adaptation. The amount of genetic variation is equally important.
Populations harbor enormous amount of variations. Allele frequencies change because of mutation, migration, genetic drift and natural selection. Some forms of natural selection maintain genetic variation. The simplest type of balancing selection is called heterosis or heterozygote superiority.
1. Sickle cell heterozygotes and resistance to malaria:
Sickle cell anemia results due to a mutation in the gene coding for beta-hemoglobin. There are three main genotypes for hemoglobin. HbA/HbA is a genotype for normal red blood cells. This genotype indicates that an individual has the normal shape of RBCs. HbA/HbS is a genotype for a sickle cell trait. This genotype is mild. HbS/HbS is a genotype for fully sickle-shaped RBCs. In an area where malaria is prevalent, heterozygotes gain an advantage. The heterozygote individuals with HbA/HbS suffer from mild anemia. However, the same genotype is beneficial for them to get protection from the malarial parasite. The heterozygote superiority inhibits the growth and reproduction of the malarial parasite. Thus sickle cell heterozygotes have a greater resistance to malaria.
2. CCR5 gene mutation and resistance to HIV:
CCR5 gene mutations develop resistance to AIDS. This gene encodes for a protein present on the surface of immune cells. Mutations in this protein prevent binding of HIV. CCR5 defined as C-C chemokine receptor type 5, is a key receptor. It can induce cellular chemotaxis. It also behaves as a costimulatory molecule in the immune synapses. The people with HIV resistance showed prevention of CCR5 expression. Anti-CCR5 strategies of the cell are strikingly marvelous. The cells with CCR5 gene mutations identify the entry of the HIV. As soon as the virus enters the cells, some of the CCR5 inhibitors get activated. The CCR5 inhibitors alter the CCR5 receptor conformations. The antibodies then bind to CCR5 and activate the process of internalization. Thus, the chemokines bind to the receptor and hide the CCR5 receptor from the virus. Thus, the virus is unable to bind to the receptor and gets eliminated.
3. HLA gene variants and resistance to malaria and hepatitis:
HLA, also known as human leukocyte antigen, is an immunogenetic component. The HLA complex helps the body to distinguish between foreign cells and own cells and proteins. These genetic variants provide resistance to diseases including malaria and hepatitis. Genes such as HLA-B and HLA-DR provide resistance to malaria. The HLA-B and HLA-DR genes are present on the sixth chromosome. The main function of HLA-DR involves the presentation of the foreign peptide antigens to the immune system. Gene variants of HLA-DR provide resistance to hepatitis B virus and hepatitis C virus.
4. Evolutionary studies in a fungal parasite:
An ecology researcher along with the team investigated the evolutionary changes occurring in a fungal parasite known as Rhizophydium megarrhizum. The parasite primarily infects the cyanobacterium freshwater species known as Planktothrix.
The scientists first studied the multiplication cycle of the fungal parasite. It multiplies rapidly once a day. The observation of Rhizophydium megarrhizum chytrids revealed the sporangial wall of this fungal strain. It simply ruptures and releases its zoospores. The fungal chytrids infect the cyanobacterial filaments. Thus the parasite penetrates into the host through the filaments and uses the nutrients for its growth. In this way, the spores mature, develop and become capable of infecting other hosts.
The experiment helped to study the adaptability to the homogeneous and diverse host population. They decided the real-time and controlled conditions to check how quickly the parasite is capable of adapting itself. The scientists enabled the conditions which would allow the parasite to adapt to the environment, keeping the host in an evolutionary standstill.
Results:
The fungal parasites adapted to genetically homogeneous hosts. Three months were enough for the parasite to get adjusted with the homogeneous host. Therefore, the fungal parasites were able to reproduce more quickly.
On the other hand, the fungal parasite could not adapt to the changes. Thus the genetic diversity in the host population slows down the adaptability of the parasites. The genetic diversity helps to develop disease resistance in the host population.
5. Genetic diversity in plants:
Genetically diverse plants showed resistance to the diseases. It also protects the plant from soil-borne pathogens and insects. Gene diversity may also help the plant to tolerate stress, drought, and infection.
References:
[1] Vogel and Motulsky's Human Genetics: Problems and Approaches, Friedrich Vogel, Gunter Vogel, Arno G. Motulsky
[2] Entry Inhibitors in HIV Therapy, Jacqueline D. Reeves, Cynthia A. Derdeyn
[3] Textbook of Pathology, V. Krishna
[4] Genetic diversity helps protect against disease, Forschungsverbund Berlin, Science Daily (With reference to Google news)
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