Final answer:
When two homozygous mice with black fur are crossed, all offspring will be black with a phenotypic ratio of 1:0. This demonstrates Mendel's Law of Segregation and underscores the importance of controlled breeding in genetics.
Step-by-step explanation:
When two mice that are homozygous for black fur are crossed, the offspring will also all be black since black fur is a dominant trait. In such a cross where both parents are homozygous (d/d), all offspring will be homozygous (d/d), resulting in a phenotypic ratio of 1:0; all offspring will display the black fur phenotype.
To observe Mendel's laws, this simple cross demonstrates Mendel's Law of Segregation, which states that alleles segregate independently of one another during the formation of gametes and are thus inherited independently of one another. There is no genetic variation in this situation as all offsprings are genetically identical with regard to the fur color trait. Controlled breeding in an experiment allows us to confirm these results.
Mendel's Law of Independent Assortment would not be demonstrated in this particular cross since both parents are homozygous for the trait in question, however, it is an important principle when considering crosses involving two or more traits. Controlled experiments like these help us understand how traits are transmitted from parents to offspring and support the fundamental principles of Mendelian genetics.