Final answer:
No single diploid organism can have all the alleles in a multiple alleles system because it can only carry two alleles for any given gene, one from each parent. Polyploidy, although common in plants, is rare and typically results in sterility in animals.
Step-by-step explanation:
No single diploid organism can have all the alleles in a multiple alleles system. In the context of genetics, a diploid organism possesses two sets of chromosomes, one set inherited from each parent. For a single gene, a diploid organism can only have two alleles - one from the mother and one from the father - even though many different alleles may exist for that gene within a population. This is because any given gene locus on a pair of homologous chromosomes can only be occupied by one allele in each chromosome.
Polyploidy
For example, when Mendel studied pea plants, he found that particular traits were controlled by two alleles—one dominant and one recessive. Now, we know his observation was an oversimplification, as multiple alleles for a certain gene can exist within a population. Each individual still carries only two of these alleles. The most common allele combination within a population is called the wild type, and any variation from this norm is considered a mutation, whether dominant or recessive.