I was wondering about what "two copies" meant. Chromosome pairs aren't copied from each other, but surely the author didn't mean to separate the DNA strand into

I was wondering about what "two copies" meant. Chromosome pairs aren't copied from each other, but surely the author didn't mean to separate the DNA strand into its mirrored halfs, that must surely not be stable whatever you do. The first reference given doesn't open without cookies enabled, so I looked it up on wikipedia instead [1]. The 3 billion number is the sum of the number of base pairs of all of the different chromosomes; i.e. the size of the genome data set that's (roughly) identical across all humans. So yes, one cell then instead has the sum of the number of base pairs of chromosomes 1..22 times two, plus the size of X * 2 or X + Y, which is approximately 2 * 3 billion. Thus the calculation is correct. [1] https://en.wikipedia.org/wiki/Human_genome https://en.wikipedia.org/wiki/Human_genome