i thought: a parent closeness to a person can be marked as 50%. seems that is 50% of all parts of dna of humans that have variability across all human population. i heard that chimpanzees are 98% close to humans by their dna, so, 100% here may match like absolute 1 or 2 % of dna.
then, if to say only about siblings with both parents same, for simplicity, a sibling also must have 50% closeness in average. then, an uncle has 50% * 50% = 25% . (because he is sibling of a parent). a cousin has 12,5%. (child of uncle). a grandfather is 25%, his sibling is 12,5%, son of his sibling is 6,25%, and grandson is 3,125%, that is, second cousin. third cousin should be 0,78125% .
and here a question appears: so, this number goes very low very quickly, when going to farther relatives. but it should not go to 0, because stranger people also must have some similar genes by chance.
so, i want to ask, what is that average level of the similar genes by chance? what is median level of it? and what is the distance between 2 of the most far persons?
i think, maybe this question is not possible to answer nowadays. because i searched, browsed in wikipedia, and saw that, seems, it is not known, to how many parts chromatids are split in meiosis. so, must be, it is not known, how much is that variability of human dna. i think, maybe this question may stay waiting for future answers.