Answer:
In genetics, a trait is considered dominant when it is expressed in the phenotype of a heterozygous individual, meaning that it only requires one copy of the dominant allele to be expressed. On the other hand, a recessive trait is only expressed when both copies of the allele are present in the individual's genotype.
To provide the best evidence that a trait is dominant, we would need to observe the trait in the phenotype of all individuals who carry at least one copy of the dominant allele. This means that if an individual has one dominant allele and one recessive allele, they should still show the dominant trait in their phenotype.
In practice, this could be demonstrated through a series of crosses between individuals with known genotypes. If the offspring of a cross between a homozygous dominant individual and a heterozygous individual all show the dominant trait, this would be strong evidence that the trait is dominant. Similarly, if the offspring of a cross between two heterozygous individuals show the dominant trait in a 3:1 ratio, this would also support the idea that the trait is dominant.
In general, the best evidence for a dominant trait would be consistent expression of the trait in the phenotype of individuals who carry at least one copy of the dominant allele. This can be observed through controlled breeding experiments and statistical analysis of the resulting offspring.