Final answer:
In a self-cross of a Yy plant, the expected proportions of offspring would show a genotypic ratio of 1:2:1 for YY:Yy:yy and a phenotypic ratio of 3 yellow:1 green seed colors.
Step-by-step explanation:
When a Yy plant is self-crossed, the expected outcome is that the offspring will exhibit a genotypic ratio of 1:2:1 (YY:Yy:yy) and a phenotypic ratio of 3 yellow:1 green, assuming that yellow seed color (Y) is dominant over green (y). This is because each parent (Yy) can contribute either a Y or a y allele, leading to four possible combinations when represented in a Punnett square. Given Mendelian inheritance, the cross will produce phenotypically identical yellow offspring from both YY and Yy genotypes due to the dominance of the yellow allele. Therefore, we expect, on average, a 75% chance that an offspring will exhibit yellow seeds and a 25% chance for green seeds.