Which of the following is true about recessive alleles?

Recessive alleles are characterized by their ability to manifest in an organism's phenotype only when two copies of that allele are present, which is referred to as being homozygous for that trait. This means that a recessive trait will not appear in the phenotype if an individual carries at least one dominant allele; the dominant allele will overshadow the expression of the recessive one. Therefore, for a recessive trait to be expressed, the organism must inherit the recessive allele from both parents, resulting in a homozygous condition.

This feature underscores the fundamental principles of Mendelian genetics, where traits are influenced by dominant and recessive alleles. The other statements do not accurately reflect the behavior of recessive alleles: they may not be more common than dominant alleles, they cannot be expressed if there is only one copy in a heterozygous state, and they can certainly be passed on to offspring even when not expressed phenotypically. This highlights the importance of the genotype in determining which traits are observable in an organism.