Question

Resistance to pesticides, antibiotic resistance in bacteria and sickle cell anaemia are examples of:

• A. Inverse mutations
• B. Natural selection
• C. Lethal genes
• D. All of the above

Answer 1

The correct option is B Natural selection

Natural selection is the process, whereby, organisms better adapted to their environment tend to survive and produce more offspring. The theory of its action was first fully expounded by Charles Darwin, and it is now regarded as the main process that brings about evolution.

Some of the examples of natural selection of the evolution on earth are- genetic basis of adaptation in 'Industrial melanism'; DDT-Resistant mosquitoes; sickle cell anaemia - persons with sickle cell anaemia are mostly found in those areas of tropical Africa, where malaria is very common.

It was reported that sickle-shaped cells of the heterozygote kill the malaria parasite.

So, the heterozygotes can resist the malaria infection in a much better way than the homozygous for the normal haemoglobin. The loss of deleterious recessive genes through death of homozygotes is being balanced by successful reproduction of heterozygotes. Thus, the natural selection has preserved it along with the normal haemoglobin in the malaria affected areas. It is an example of balancing or stabilizing selection. Antibiotic resistance in the microbes - Joshua Lederberg and Esther Lederberg showed the genetic basis of adaptations in bacteria by culturing bacterial cells by their plating experiment.

Thus, option B is correct.