|From 1856 to 1865, Mendel
bred and raised pea plants, having had some training in statistics. He
knew he had to study large numbers of plants, so he identified traits in
thousands of plants. The patterns he found in his experiments formed the
basis of our present knowledge of genetics.
He started his experiments by breeding plants
that were pure for each trait. Parent plants that are pure (homozygous)
always produce offspring with that trait. He obtained a total of 14 pure
strains. One for each of seven pairs of contrasting traits. He cross pollinated
the plants by hand. He crossed pure tall plants to pure short plants. Pure
wrinkled seeded plants with pure smooth seeded plants, etc. When the plants
seeded, he grew large numbers of these and recorded how many and what kinds
of plants grew.
1. Mendel's first hypothesis was that inherited
characteristics are controlled by factors that occur in pairs.
2. Mendel's second hypothesis stated that one
factor (dominant) in a pair mask the other (recessive) preventing it from
showing its affect.
|3. The third hypothesis
is that each offspring receives only 1 factor from each parent.
4. The fourth hypothesis is that different factors
are inherited separately (such as seed color does not have any connection
with the height of a pea plant).
Mendel called the original parents P1 for parent
generation and the offspring of the cross F1 for the first filial generation.
He called the next cross F2 for second filial generation.
When Mendel crossed tall pea plants with the
short pea plants of the P1 generation, all of the F1 plants were tall.
The same thing happened with each of the seven traits, only one form of
each characteristic appeared in the F1 plants.
To find out where the characteristic for short
plants had went, he crossed the F1 plant to the F1 plant to get F2 plants,
in which appeared the short plants again.
Not only did it reappear but with a certain predictable
mathematical relationship, 1 short and 3 tall. The same relationship, also,
showed up for all of the seven traits.