One character in peas that mendel studied was yellow versus green seeds. a cross between a homozygous yellow line (yy) and a homozygous green line (yy) will result in f1 plants that are heterozygous (yy) for this trait and produce yellow seeds. when an f1 plant undergoes meiosis, what gamete types will it produce, and in what proportions

The proportions will be 1/2Y and  1/2y.
An F1 hybrid is the first filial generation of offspring of distinctly different parental types. F1 hybrids are used in genetics, and in selective breeding, where it may appear as F1 crossbreed. Meiosis is the type of cell division where a parent cell divides to yield four haploid daughter cells in the gametes. When the F1 plants undergoes meiosis since they are heterozygous (Yy) they will yield gametes with either Y or y allele.