Which is the largest known gene in humans?

$A$: $SNPs$ (pronounced as "snips") are common in the human genome.
$R$: These are minute variations that occur at a frequency of one in every $300$ bases.

The number of nitrogenous bases in the human genome is approximately ...... .

In addition to the human genome sequence,draft or finished genome sequences existed for eight model organisms by $2002$. Which of the following organisms are not the part of that group of eight model organisms?

How many genes are present on the $Y$ chromosome?

How many locations have been identified in the human genome where single base differences occur?