Your genes come from your parents, of course.
And from their parents. And from their parents' parents.
And well... you get the idea.
You have two sets of 23 chromosomes.
One set from each parent.
For almost every chromosome you inherit from your mohter,
You also inherit one from your father.
That has his versions of the same genes.
Together they form a pair of homologous chromosomes.
The X and Y chromosomes however, are special.
Usually, females have two X chromosomes, while males have and X and a Y.
You get one of your X chromosomes from your mother.
Whether you get your father's X chromosome or his Y chromosome,
determines your sex.
Most adult cells contain two sets of chromosomes,
but sperm and egg cells have only one set of 23 chromosomes each.
When the body forms sperm or egg cells, a cell divides and pairs of chromosomes separate.
A random member or each pair moves into each new cell.
This is why when you were concieved,
you obtained half of you mother's genes
and half of your father's genes
but your siblibngs didn't necessarity get the same versions of your parents' genes
that you did,
unless you happen to be and identical twin.
To form sperm or egg cells, your chromosomes double
like so.
When the homologuos pairs seperate, sometimes they cross over
and at seemingly random points, exchange DNA.
This is called genetic recombination.
Because your genes get shuffled during recombination,
the chromosomes you pass along to your children
are not exactly the same as the ones you inherited from your parents.
This makes it hard to use most of your chromosomes
to trace your geneology back very far.
However, most of the Y chromosome is handed down
from father to son entirely intact.
Likewise, in humans, DNA in the mitochondria
is passed on only from mother to child.
For this reason ancestry along your father's line,
or your mother's line is easier to trace using the Y chromosome
or mitochondrial DNA.
When sperm and egg cells join together at fertilization,
they create a single cell with two complete sets
of 23 chromosomes, one set from your mother
and one from your father.
This single cell will divide to create new cells
over and over until it creates a child.

Genetics 101 Part 3: Where do your genes come from?

Genetics 101 Part 3: Where do your genes come from? : Find out how chromosomes and genes are passed down from parent to child.