Monohybrid crosses: The F1 Generation

Mendel’s first experiments were monohybrid crosses (mono = one, hybrid = combination), where parents that differ in a single trait are crossed to produce hybrid progeny. For example, a round seed line was crossed to a wrinkled seed line, and the resulting progeny were found to all have round seeds. Since all the hybrid progeny had the same phenotype as the round seed parent, round seeds are said to be dominant over wrinkled seeds, which are recessive.

P   round seed line x wrinkled seed line  
F1   round seed progeny  
Conclusion: Round seeds are dominant to wrinkled seeds

The other traits that Mendel studied followed the same pattern. Yellow seeds are dominant to green seeds. Purple flowers are dominant to white flowers. In these crosses, the original parents are the parental, or P generation, and their progeny are the F1 generation (for 1st filial; filial = son or daughter). An “x” stands for, “is crossed to” and an arrow indicates progeny of a cross.

Mendel also showed that reciprocal crosses, which are two crosses that differ only in the sex of the parents, give identical results. For example, in a cross between a round seed plant and a wrinkled seed plant, it makes no difference whether the pollen comes from the round seed plant or the wrinkled seed plant. Since the sex of the parent doesn’t matter for these crosses, the term “gamete” is often used to refer to a generic reproductive cell (pollen/sperm or ovule/egg).

P round seed pollen x wrinkled seed ovule   round seed ovule x wrinkled seed pollen
  arrow   arrow
F1 round seed progeny   round seed progeny
Conclusion: reciprocal crosses give identical results