In his first cross to create the hybrid
plant Mendel ended up with NO recessive traits
for seed shape. But when he crossed the
offspring because they where heterozygous for
that trait he ended up some having the
recessive trait, some having the homozygous
trait and some continuing the heterozygous
trait.
In correct breeding terms his first cross
between the plants is called the F1 cross or F1
generation. The breeding out of those offspring
is called the F2 cross or F2 generation.
Now since he has Ss, ss and SS to work with
you can probably do the punnet square for each
to see how they will work out. It would be a
good time to test your knowledge on this.
Compare your results with what you have learned
about ratios in this chapter and you will be
able to see how it all fits together. It is
really very simple once you know a few
rules......but like most things there are
exceptions to the rules.
Back to frequencies:
We know that if two heterozygous parents
are crossed that the ratios will be 50/50 with
regards to the allele (Remember the genotype
can be Ss, SS or ss, but the allele is either S
or s. Look at the table below when we cross two
