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A recessive allele is defined as one that must be present in two copies (homozygous condition) to manifest its influence on the organism's phenotype. This means that for a trait governed by a recessive allele to be visible in the phenotype, both alleles at the corresponding locus on the chromosomes must be recessive. For example, if an individual possesses one dominant allele and one recessive allele, the dominant trait will be expressed, demonstrating that the recessive allele does not have a direct effect in that instance unless it is paired with another recessive allele.

This understanding is fundamental in genetics, especially when exploring inheritance patterns, as it helps clarify how traits are passed down through generations and how genotypes correspond with phenotypes. The interactions between dominant and recessive alleles are crucial for predictive models in genetics, including Punnett squares, which illustrate potential offspring traits based on parental genotypes.