Ablack mouse mates with a brown mouse, why are no brown offspring produced

Because the black mouse is homozygous.

The black color in mouses is dominant, and the brown is recessive. When a parent is homozygous, their children need to have their gene. Because in this case the trait is black, it dominates brown in all children.

The table is BB×bb = Bb, Bb, Bb, Bb = 100% heterozygous genotype = 100% black phenotype.

The black mouse has a dominant gene and the brown mouse has a recessive gene

Thermoclines are typically found in bodies of water such as lakes or rivers that serve as a "transition layer" between the mixed layer of the upper part of the ocean, the epipelagic zone, and the colder layer of the ocean located at the bottom, the mesopelagic zone. It is important to the organisms living in the ocean.