Final answer:
The expected proportion of heterozygotes among the F2 offspring in a monohybrid cross is 1/2.
Step-by-step explanation:
In a monohybrid cross, the expected proportion of heterozygotes among the F2 offspring is 1/2. This can be explained by considering the genetic makeup of the parents in a typical monohybrid cross. When two heterozygous individuals (Aa x Aa) are crossed, the F1 generation will include offspring with three possible genotypes in a predictable ratio: one quarter will be homozygous dominant (AA), half will be heterozygous (Aa), and one quarter will be homozygous recessive (aa). Therefore, the heterozygotes will make up half of the F2 offspring.