How many pairs of chromosomes are present in human beings (in $pairs$)?

What are the organs called that perform different functions but have a similar basic structure?

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

If fossils of an organism are found in the deeper layers of the Earth,what can we predict about its extinction?

Two pea plants,one with round green seeds $(RRyy)$ and another with wrinkled yellow $(rrYY)$ seeds,produce $F_1$ progeny that have round,yellow $(RrYy)$ seeds. When $F_1$ plants are selfed,the $F_2$ progeny will have new combinations of characters. Choose the new combinations from the following:
$(i)$ Round,yellow
$(ii)$ Round,green
$(iii)$ Wrinkled,yellow
$(iv)$ Wrinkled,green

In which animal did the eyes originate first?