Two Copies of the Genome
You Inherit One Copy From Each Parent
A person has two copies of every gene sequence, one inherited from the mother,
and the other inherited from the father. A child thus inherits one copy from
each parent's own pair, and this copy is selected from the parent randomly. In
order to fully understand a person's DNA sequences, both inherited copies of
a gene need to be examined.
These sequences are often not identical. Gene sequences
for so-called "dominant" traits are expressed over "recessive"
traits. Do you have a cleft chin? It is an indentation
at the tip of your chin. If so, you have at least one
copy of the dominant gene for cleft chin. But if your
chin has no indentation, you have two copies of the recessive
gene for this trait.
Two Copies of Each Chromosome
You inherit one copy of every chromosome from each parent. Therefore you have two copies of every gene sequence.