Basic mendelian genetics, relatedness to brother and terms of percent genes shared pic or graph appreciated?

Question

Me and my friend were having an argument about genetic relatedness between brother and sister, aunt and cousin. He thinks that brother and sister are 100% related in terms of genes while I try to tell him that we receive 50% random genes from each parent giving each sibling only a 50% relatedness.

I also remember some interesting facts about genetic relatedness between ant sisters being higher than the relatedness to their mother, 66% for sisters, 50% or less (not sure for mother)

Can someone find me some concrete evidence from a reputable source backing up all these facts which I am 100% sure are true.

How do you take into account higher frequencies of dominant to recessive genes, as those work at a 3:1 ratio. Can you also have two dominant genes with a different phenotype end in a frequency of 50%?

This is basic genetics people, someone must have an answer, I left my book at home, easy 10 points to an educated person in science and anthropology.

Answer 1

The only way you are 100% related is you have an identical twin.  You aren't likely going to be exactly 50% either.  I imagine it would be a natural distribution with 50% as the mean.  Some siblings would by chance have received more of the same chromosomes than others.  Some would be less than 50% the same.  You would be about 50% the same as each parent but not necessarily with your siblings.