A gene for the MN blood group has codominant alleles M and N. If both children in a family are of blood type M, which of the following situations is possible?

You cross two true breeding lines of petunia. One produces red flowers and the other white flowers. The F1 

offspring all show pink flowers. You conclude from this that:

If you look at a blood sample from a person who is heterozygous at the sickle cell locus you will see both normal circular red blood cells and sickle-shaped red blood cells. This is an example of

The number of different alleles for ABO blood types is _____ resulting in _____ different blood types.