In human females, meiosis­-$II$ is not completed until

Ejaculation of human male contains about $200 -300$ million sperms, of which for normal fertility ____ $\%$ sperms must have normal shape and size and at least ____$\%$ must show energetic motility.

$A$ : Middle piece of sperm is called powerhouse.
$R$ : It contains mitochondria.

Meiotic division during oogenesis is different from that in spermatogenesis. Explain how and why ?

In humans, at the end of the first meiotic division, the male germ cells differentiate into the