For normal fertility,what percentage of sperm must have normal shape and size (in $\%$)?

The testes of a great majority of mammals are typically enclosed in an extra-abdominal sac,the scrotum. The temperature inside the scrotum is lower than that in the abdomen. What will happen if the temperature of the scrotum is artificially maintained at the level of abdominal temperature?

Where are $Sertoli$ cells found?

What is observed during the first meiotic division of oogenesis?

The termination of the process of oogenesis is indicated by the formation of . . . . . . .

What happens upon the fertilization of the egg nucleus with the sperm nucleus?