Dominant traits are characteristics that are expressed in an organism when at least one dominant allele is present in its genetic makeup. In genetics, alleles are different forms of a gene, and dominant alleles can mask the effects of recessive alleles. For example, in Mendelian inheritance, a trait like brown eyes is often dominant over blue eyes. These traits can be observed in various organisms, including plants and animals. In humans, dominant traits can include features like curly hair or the ability to roll one's tongue. Understanding dominant traits helps in fields like genetics and breeding, where predicting traits in offspring is important.