The first law of Mendel, known as the Law of Uniformity, establishes that when two individuals homozygous for opposing traits are crossed, the offspring of the first generation (F1) will be heterozygous and will only show the phenotype of the dominant parent.
All descendants will share similar characteristics, demonstrating uniformity in phenotype.
This law lays the groundwork for understanding genetic inheritance and allele segregation, providing a crucial foundation for classical and modern genetics.