Mark the odd one (w.r.t. true breeding line).

In his classic experiments on pea plants, Mendel did not use

Mendel observed that all $F_1$ progeny plants:

Mendel's work remained unrecognized for a long time due to:
$I.$ Communication was not easy.
$II.$ The concept of factors which did not blend was not accepted.
$III.$ The use of mathematics to explain biological problems was unacceptable.
$IV.$ He could not provide any physical proof for the existence of factors.
Choose the right combination.

Which of the following is the functional unit of inheritance?

Which of the following traits was $NOT$ selected by Mendel in his pea plant experiments?