Final answer:
Haploid cells are essential in sexual reproduction to maintain chromosome number in offspring. They combine to form a diploid zygote with the right amount of genetic material, avoiding chromosome doubling over generations.
Step-by-step explanation:
It is important that the cells that combine in sexual reproduction are haploid cells and not diploid cells to ensure the correct number of chromosomes in the offspring. During sexual reproduction, haploid gametes from two parents unite during fertilization to form a diploid zygote. This process ensures that the zygote has the correct number of chromosomes, preventing an exponential increase in chromosome number in subsequent generations. The process that results in haploid cells from diploid cells is called meiosis, which involves two cell divisions and produces cells that are genetically unique due to crossover events and random assortment of chromosomes.