$(a)$ What is the location of the following :
$(i)$ $DNA$ in a cell
$(ii)$ Gene
$(b)$ Expand $DNA$.

$(a)$ List two reasons for the appearance of variations among the progeny formed by sexual reproduction.
$(b)$ $(i)$ Name the part marked '$A$' in the diagram.
$(ii)$ How does '$A$' reach part '$B$'?
$(iii)$ State the importance of the part '$C$'.
$(iv)$ What happens to the part marked '$D$' after fertilisation is over?

How can pregnancy be prevented surgically?

Give the respective scientific terms used for studying:
$(i)$ The mechanism by which variations are created and inherited,and
$(ii)$ The development of new types of organisms from existing ones.

Would a Planaria cut vertically into two halves regenerate into two individuals? Complete Figure $D$ and $E$ by indicating the regenerated regions.

Why is the temperature of the scrotal sac $2\,^{\circ}C$ less than the body temperature?