Family Math

How  you relate to your primary relatives:

Your mom:  You got 23 chromosomes from your mom.  22 autosomes and 1 X chromosome. You also got your mitochiondria, therefore your mtDNA, from your mom.   You are 1 generation separated from your mom.

Your dad: You got 23 chromosomes from your dad.  If you are a man, you got 22 autosomes and your Y chromosome from your dad.   If you are a woman, you got 22 chromosomes and your second X chromosome from your Dad. You are 1 generation removed from your mom.

Important concept here: If you are a woman, the X chromosome you got from your dad did NOT cross-over in him.  It is a nearly exact copy of the chromosome that your paternal grandmother passed to your dad.  It is a cross-over hybrid of your great grandfather's and your great grandfather's X chromosome.  LIke a little time capsule, but in DNA,

Your siblings: Cross-overs happen every time a sperm or an egg is made, but they are different every time.   You may get the tip of your grandfather's chromosome 1, while your brother got the tip of your grandmother's.  On average, full siblings share 1/2, or 50%, of their DNA.