My older brother had his DNA history done through 23&me. That’s just like me having my DNA done I would think. Maybe I’m wrong but wouldn’t we have the identical DNA?
Not identical but close. In these tests, they determine relationships based upon "centimorgans." My son shares about 3400 centimorgans with me. A full sibling will share b/w 2400-2800 normally (2200-3200 max range).
You will share about HALF of the DNA of your parents.
No. You have unique DNA from anyone but an ID twin.
It’s the combos they look for.
But, mitochondrial DNA specifically, is the same for you both. It is passed from mother to mother, and stops as a result with males. You will not pass on yours. I pass on mine, the same as my mom and her mom and her mon - but it ends with my son. :-D
DNA of brothers would tend to be very similar especially if the milkman and the postman were identical twins.