Even before the baby is born, watching his parents, we can predict many of the biological features that it will have.
This is possible because we know the laws of the legacy.

Dominant and Recessive Traits

For example, if one parent has brown eyes, and the other blue, the child will have brown eyes. 
If both parents have blue irises, the child and parents have blue eyes. If one parent has curly hair, the child will have an equal chance of inheriting curly hair and blue to succeed.
However, the laws of inheritance in man are sometimes very complex. 
If the father has characteristics very different from the characteristics of the mother, then one of two opposite tendencies override other and the child will report the characteristics of one parent and not from the other.

That distinction which prevails is called dominant and the other recessive or suppressed. Brown eyes are dominant hereditary qualities, and the blue recessive. That’s why the child in our example will have brown eyes.

How are these qualities transferred from parents to a child? 

They are transferred within the nucleus of the egg cell and the nucleus of the seminal cells. The nucleus is composed of a large number, perhaps hundreds, of particles called genes.
Genes are not scattered at random in the nucleus, but are connected in series, a string of beads.

Mature egg cell has a series of 24 such genes, just as there are a mature seed cells.
When the egg and semen cells are connected together, they get along 24 pairs of these arrays which are called chromosomes.

Genes, even in one and the same chromosome, differ in terms of their impact on development.
Some manage the development of one, the other the development of other organs or body characteristics.
Yet, they all participate in joint development of the whole body.
The characteristics of the burden inherit one set of genes together, but sometimes strings can break and can reach mutual exchange of particles with other arrays.