Filariasis also called elephantiasis is caused by Wuchereria bancrofti or filarial worm. It spreads by bite of Culex mosquito.

Haemophilia is the most serious and notorious disease which is more common in man than in woman. The person which contains the recessive gene for haemophilia lacks normal clotting substance (thromboplastin) in blood so, amino injuries cause continuous bleeding and ultimate death. It is X-linked disease.

Active immunity involves the active functioning of the person's own immune system which leads to synthesis of antibodies and or the production of immunologically active cells.

Haemophilia-A is characterized by lack of antihaemophilic globulin (factor VIII). Haemophilia is caused due to X-linked recessive gene.

Natality or birth rate is the rate of production of new individuals per unit of population per unit time through birth. Natality is expressed as $\frac{∆{\mathrm{N}}_{\mathrm{n}}}{∆\mathrm{t}}$ and $\frac{∆{\mathrm{N}}_{\mathrm{n}}}{\mathrm{N}∆\mathrm{t}}$ = Specific natality rate.

Down's Syndrome is Trisomy of 21^st chromosome. It is characterized by mental retardation, short stature with stubby fingers and heart defects.

In passive immunity, antibodies from one individual are passed into another individual. They give immediate protection unlike active immunity which takes a few days or weeks to build up. However, it only provides protection against infection for a few weeks.

A particular gene has been found to occur in two alternative forms or allelomorphs. The existence of more than two allelic forms of a gene is called multiple allelism and the alleles as multiple alleles, eg, blood group in human.

There are three main router for transmission of HIV, ie, AIDS virus. These are through sexual intercourse, transmission through blood transfusion, blood products, contaminated equipments, and from mother to baby. Infected needles and syringes (ie, equipments) are most efficient method of HIV infection.

Ecosystems are made up of biotic and abiotic components. Cave ecosystem is incomplete because it does not have all the biotic and abiotic (specially) components.