Final answer:
An organism expresses a recessive gene when it is homozygous for that gene. The genotype of an organism can be determined by observing whether it consistently exhibits the recessive phenotype.
Step-by-step explanation:
A recessive allele is only expressed when an organism has two copies of the recessive gene. In other words, the organism is homozygous for the recessive gene. The genotype of an organism can be determined by observing whether it expresses the recessive phenotype consistently across multiple generations. If an organism consistently exhibits the recessive phenotype, it is likely homozygous for the recessive gene.