What distinguishes dominant alleles from recessive alleles?

Dominant alleles are characterized by the ability to express their traits when present in just one copy, which means they can overshadow the effects of a recessive allele. This means that if an individual has one dominant allele and one recessive allele for a particular gene, the dominant allele will determine the phenotype, or observable traits, of that individual.

On the other hand, recessive alleles need two copies—one from each parent—to manifest their traits. If an individual carries only one copy of the recessive allele along with a dominant allele, the recessive trait will not be expressed. This relationship is key in understanding how traits are inherited and how phenotypes appear in offspring based on the alleles they inherit from their parents.

This distinction is foundational in genetics, as it explains many of the inheritance patterns and traits seen in organisms. It also underscores the significance of heterozygous (one dominant and one recessive allele) versus homozygous (two identical alleles) genotypes in determining physical characteristics.