Final answer:
A heterozygous organism has two different alleles for a trait. This means that the alleles inherited from each parent are not identical, with one usually being dominant over the other. Being heterozygous impacts the phenotype of an organism and its potential genetic contributions to offspring.
Step-by-step explanation:
A heterozygous organism has two different alleles for a trait. When discussing genetics, diploid organisms, like humans, inherit two alleles for each gene, one from each parent. These alleles could be either identical, in which case the organism is homozygous, or different, which defines a heterozygous state. Therefore, the correct answer to the student's question is that a heterozygous organism has two different alleles for a trait.
In a genotype consisting of two different alleles, one is typically dominant and the other recessive. This has implications on the organism's phenotype, which is the observable expression of a trait. Even if the recessive allele is not expressed when heterozygous, it can still be passed down to the next generation. Understanding the concepts of homozygosity and heterozygosity is crucial for explaining the genetic mechanisms underlying inheritance patterns elucidated by Mendel's laws of inheritance.