Introduction to heredity

 Heredity is inherited from traits from parents.

Some traits seem to dominate, like skin colour, hair colour, and height. 
The study of what gets passed on via genes was much, much older than the study of DNA.
The father of heredity study is Gregor Mendel who was actually a monk and he would experiment with plants and see which plant would follow which parent DNA more.

Certain traits are more prominent than others. An Allele and a Gene are very different and have defining characteristics for both, Gregor mentally was doing this in the 1850s.

Let's take two random chromosomes from the father, and mother, and on the chromosomes is a Locus, which is where the gene for the eye colour comes from, and let's say these are Homologous chromosomes, so they code for the same allele.
Now if both parents have different eye colours the person would be a heterozygote. Which is a heterozygous genotype. If both parents have the same eye colour of genes the person is a  homozygous, or this a homozygous genotype.

But Mendel discovered and learned something we will call dominance, this refers to one of the traits inherited from the mother or father is the more dominant gene. Now let's take two genes: One having blue eyes (the more dominant gene), and the other having brown eyes (the recessive gene).
And since brown eyes are the dominant gene, most of the people who have both genes will most commonly have brown eyes, which is named a Genotype.

Now a Phenotype, for example, let's say you have a brown eye allele from both parents. You will see that you will have brown eyes.