Introduction:
Determining the genotype of an individual with a dominant phenotype can be done by applying the principles of Mendelian genetics. The genotype refers to the genetic makeup of an individual, while the phenotype refers to the physical expression of the genes. In the case of a dominant phenotype, the individual displays the dominant trait, but the underlying genotype can be either homozygous dominant (two copies of the dominant allele) or heterozygous (one copy of the dominant allele and one copy of the recessive allele). To determine the genotype, several approaches can be used.

1. Observing the Offspring:
If the individual with a dominant phenotype is crossed with an individual showing the recessive phenotype for the same trait, the resulting offspring can provide valuable information about the genotype of the parent with the dominant phenotype. If all the offspring display the dominant phenotype, it suggests that the parent with the dominant phenotype is homozygous dominant (DD). On the other hand, if some offspring display the recessive phenotype, it suggests that the parent with the dominant phenotype is heterozygous (Dd).

2. Test Cross:
A test cross involves crossing the individual with a dominant phenotype with an individual displaying the recessive phenotype. If all the offspring display the dominant phenotype, it suggests that the individual with the dominant phenotype is homozygous dominant (DD). However, if some offspring display the recessive phenotype, it suggests that the individual with the dominant phenotype is heterozygous (Dd).

3. Punnett Square:
Using a Punnett square can also help determine the genotype of an individual with a dominant phenotype. By knowing the phenotype of the individual and the phenotypes of its parents, the possible genotypes can be deduced. For example, if both parents display the dominant phenotype, their genotypes could be either homozygous dominant (DD) or heterozygous (Dd).

4. DNA Testing:
Advancements in molecular biology have made it possible to determine an individual's genotype through DNA testing. This involves analyzing the DNA sequence to identify the specific alleles present. By comparing the individual's DNA with known DNA sequences, it can be determined whether the individual is homozygous dominant (DD) or heterozygous (Dd) for the trait.

Conclusion:
Determining the genotype of an individual with a dominant phenotype can be achieved through various methods, including observing the offspring, performing a test cross, using a Punnett square, or conducting DNA testing. These approaches provide valuable insights into the underlying genetic makeup and can help understand inheritance patterns and predict the likelihood of passing on specific traits to future generations.