The harmful allele of sickle-cell anaemia has not been eliminated from human population. Such afflicted people derive some other benefit. Discuss.
Sickle-cell anaemia still persists in the population despite being harmful because this mutation can also be beneficial in certain conditions.
The mutant $\mathrm{Hb}^5$ type haemoglobin is found at high frequencies (up to $20 \%$ and above) in the tropical Africa.
It is known that heterozygotes $\left(\mathrm{Hb}^{\mathrm{s}} / \mathrm{Hb}^{\mathrm{A}}\right)$, having both types of haemoglobin show resistance to malarial infection because the body targets the Plasmodium falciparum infected cell for destruction. In contrast, individuals homozygous for normal haemoglobin $\left(H b^A / H b^A\right)$ suffer high mortality rates in early childhood due to malarial infection.
Thus, the allele for sickle cells has been maintained because heterozygotes have a higher reproductive success than either of the two possible homozygotes.
Lymph nodes are secondary lymphoid organs. Explain the role of lymph nodes in our immune response.
Lymphoid Organs immune system of human beings consists of lymphoid organs. The organs whereas callid the maturation and proliferation of lymphocytes occurs are called lymphoid organs. Lymphoid organs are of two types. These are
Lymph nodes are small solid structures present at different points along the lymphatic system. They trap the microorganisms or other antigens that enter the lymph and tissue fluid. Antigens trapped in the lymph nodes activate the lymphocytes and produce an immune response.
Why is an antibody molecule represented as $\mathrm{H}_2 \mathrm{~L}_2$ ?
Each antibody molecule has four peptide chains, two small called light chains (represented by L ) and two longer called heavy chains (represented by H ). Hence, an antibody is represented as $\mathrm{H}_2 \mathrm{~L}_2$.
What does the term 'memory' of the immune system mean?
When the body encounters a pathogen for the first time, it mounts an immune response by generating antibodies. This response is of low intensity. Subsequent encounter with the same pathogen elicits a highly intensified secondary response.
This is ascribed to the fact that our body appears to have memory of the first encounter. This type of secondary immune response is elicited by memory T-cells, B-cell which keep ready to mount a rapid and vigorous attack as soon as the same pathagen infects the body again.
If a patient is advised anti restroviral therapy, which infection is he suffering from?
Name the causative organism.
The patient is suffering from AIDS. The causative agent is HIV virus, a member of 'retrovirus group'.