The maleness of a child is determined by

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

$(a)$ Why do we say that homozygous plants produce pure progeny?
$(b)$ Define heterozygous.
$(c)$ Explain how the process of speciation takes place.

$(a)$ "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.

New species may be formed if
$(i)$ $DNA$ undergoes significant changes in germ cells
$(ii)$ chromosome number changes in the gamete
$(iii)$ there is no change in the genetic material
$(iv)$ mating does not take place

On which of the following plant species has Mendel worked?