A gamete contains one set of chromosomes
This character trait is known as homoplasy. the definition of homoplasy that two or more species share a character, but they did not descend from a common ancestor.
This trait is known as convergent evolution, or convergence.
YY and Yy would result in a plant with yellow seeds. This is because Y is dominant and yellow seeds would show with a dominant homozygous and a heterozygous. It can't be yy because that would be homozygous recessive