Biological features and characteristics come down from parents to children, from children to their children. This whole process is called heredity.
The subject that studies the mechanism of heredity, is called genetics. The characteristics that decend down from parents to children, are called genetic materials, and the unit that transmits these information are called genes.
Genes specify the amount and kind of proteins to construct. These proteins are what distinguishes certain organisms.
Biological characteristics include colors of skin, eyes, and face, height, physical strengh, ..., for physical characteristics, aggressiveness, passivity, liveliness, gloominess, hot temperedness, patience, ..., for mental characteristics.
However, these characteristics are not all controlled by heredity, but also altered by the surrounding atmosphere in which the child is brought up in. For example, it can be said that the child's actions are similar to its mother because of heredity, but also because the child was brought up watching and imitating its mother. For instance, language is not something you are born with, but something you achieve from your surrounding atmosphere and education.