Down's syndrome is caused by an extra copy of chromosome number 21. What percentage of offspring produced by an affected mother and a normal father would be affected by this disorder ?

Two crosses between the same pair of genotypes or phenotypes in which the sources of the gametes are reversed in one cross, is known as : -

Pattern baldness, moustaches and beard in human males are examples of : -

Which one of the following conditions though harmful in itself, is also a potential saviour from a mosquito borne infectious disease ?