What are the differences that arise among organisms of the same species called?

How can the chromosomes be identified?

What is molecular phylogeny?

It is a commonly held misconception that the mother's egg is responsible for determining whether the baby will be a boy or a girl. But actually,it is the father's sperm that decides this. Which of the following makes the sperm the decisive factor?

List three main factors responsible for the speciation and briefly describe each one of them.

$(a)$ "Recent fossils are found closer to the earth's surface." Comment on the statement stating reason.
$(b)$ List two factors which could lead to the rise of new species.