A punnet square is used to visually see the dominant and recessive traits. Mendel's law says that alleles pair independently during the formation of gametes (aka sex cells). This means that traits are transmitted to offspring independently of one another.
No blacks are 100% human.. people are black because of the pigments in your skin. That is why we have light skins and dark skins not because light skins are more human than dark skins.
