white flowers. So there were alternate forms
or alleles of the same genes. So later Mendel
came along and the key for him was his background
in mathematics. Mendel was a very well-schooled
man and he could put together his understanding
of science with his understanding of mathematics
and makes some predictions about what might
have been going on and this is where he came
up with the concept that there were two alleles
for the same character perhaps or maybe even
more. But he was examining two alleles and
that is where we will explore for this time.
Why is that that Mendel chose to work with
pea plants? First of all, there are many variations
of pea plants, many variations within pea
plants. In addition, there had already been
previous work in which plants had been hybridized.
They are easy to grow and they don't take
a lot of time to grow. In addition, they were
capable of self-fertilizing and with some
modifications, cross fertilizing. Mendel
had ultimate control of his model of study.
Let us take a look to start with at the pea
plant and how self-fertilization might happen
versus cross-fertilization. First of all,
it is key to understand that the pea plant
has both male and female components in its
flower. So it has anthers, which contain pollen
under the male as well as carpels, which contain
the female ovule. Now self-fertilization would
be the normal case. So you could easily self-fertilize
by pollen coming from the anthers and brushing
straight on to the carpels of that same flower.
Mendel though wanted to be able to cross fertilize
that as well as self fertilize and in this
case, he would take pollen from one true breeding
plant and apply it another true breeding plant.
Because he was able to remove the anthers,
he could stop self fertilization. He would
take the pollens say here from the white plant
and paint it on the carpels of the purple plant
who had had its anthers removed and he would
look at the progeny. In this case, they all
came out looking like the purple flowers.
Mendel could also perform reciprocal crosses.
Reciprocal simply means doing it the other
way round in which case he would be taking
pollen from a purple flower and applying it
to a white flower who had had its anthers
removed and he noticed we have the same outcomes.
So he chose seven true breeding traits that exhibited
segregation. There is a little controversy
as to why he didn't he chose other traits,
but the other here is that he chose seven
traits that showed this pattern where the
one phenotype or the appearance disappeared
and then reappeared in the next generation.
The seven phenotypes that he chose were seed
shape either round or wrinkled. We had seed
color yellow or green. And flower color purple
or white. Pod shape. We also can look at pod
color and whether a plant is tall or short
and then the flower position on the plant.
These are traits that he noticed this very
same pattern happening with. In the parental
generation or the P generation, he would take
true breeding parents one that is true breeding
purple and one that is true breeding white
and by true breeding, we mean pure breeding.
He would cross them and cross them and cross
them and make sure they were only purple and
make sure they were only white. That is what
true breeding meant. He would cross those
and what we call the F1 cross and become an
F1 generation. Cross-fertilization happens
and all of the F1 generation look just like
one of the parents and when we self-fertilized
the offspring from the F1 generation, they
will produce phenotypes or appearances where
the parent phenotype that went missing shows
up again. And so whether he was dealing with
round or wrinkled seed or yellow or green
seeds, the same pattern of inheritance was
exhibited and that is why he chose those traits.