Explanation:

Law of Dominance:
- The Law of Dominance states that in a heterozygous individual (having two different alleles for a particular trait), only the dominant trait is expressed.
- Dominant traits mask the expression of recessive traits in the F1 generation.

Gene Expression:
- Genes are segments of DNA that code for specific traits.
- Each gene has two alleles, one inherited from each parent.
- The dominant allele is expressed in the phenotype of an individual, while the recessive allele remains hidden.

Genotype and Phenotype:
- Genotype refers to the genetic makeup of an individual, i.e., the combination of alleles present.
- Phenotype refers to the physical expression of the genotype, i.e., the observable traits.
- In the F1 generation, individuals possess two different alleles for a trait, but only the dominant allele is expressed in the phenotype.

Mendelian Inheritance:
- The principles of inheritance discovered by Gregor Mendel explain the patterns of genetic inheritance.
- Mendel's experiments with pea plants demonstrated the segregation of alleles during gamete formation and the dominance of certain traits.

Punnett Square Analysis:
- Punnett squares are used to predict the genotypes and phenotypes of offspring based on the parental genotypes.
- In the F1 generation, the Punnett square shows that individuals carry one dominant allele, resulting in the expression of dominant traits.
Therefore, the traits in the F1 generation only express the dominant trait due to the Law of Dominance, gene expression, genotype-phenotype relationship, Mendelian inheritance principles, and Punnett square analysis.