did Mendel discover the principles of heredity?
Mendel's success depended on several things:
he picked a simple system (pea plants)
that reproduced rapidly.
he kept records on the traits of
each plant and then took pollen from one plant to fertilize
the flowers from another plant and saw predictable patterns
in the offspring plants.
did Mendel discover?
Try to see these results as Mendel did, not knowing what is happening
to cause the results. For example, Mendel first grew purebred lines
of green peas and yellow peas. Then he took pollen from a green
pea plant, smeared it on the flowers of a yellow pea plant, and
saw that the new peas were always green.
What happened to the yellow trait?
Did the traits that control yellow somehow disappear? How about
the possibility that they were still there in the offspring but
their influence was hidden by the more dominant green trait (see
table below)? Mendel suspected that the trait for green was dominant
over that for yellow because some of the next generation's
peas were yellow! And this occurred in a consistent ratio of three
green pea plants for every yellow one.
did this happen?
Things only made
sense to Mendel if he assumed that each trait had TWO "controllers,"
and that the sex cells carried only one of the two controllers.
Assuming that, Mendel could make a chart like the one below: