48
And he answered the question of where that fusion occurred. You see, he made a prediction based on the chromosome numbers that two pairs fused into one pair.
Then he looked at our chromosomes and found where the fusion occurred and why we know it was a fusion.
Usually, chromosomes have one centromere and two telomeres ( repeated sequences of DNA) at both ends. In human chromosome 2, however, there are two centromeres ( one inactive) and three telomeres, one in the middle of the chromosome and twice as big as usual. This is exactly what would be expected of there was a merge. Furthermore, we can compare the genes on those chromosomes with those on chromosomes in chimps and determine which chimp chromosomes merged to make human chromosome 2.
Finally, there is no reason why there would be two centromeres and three telomeres unless two chromosomes merged.
So we have the following sequence of events: it was found that humans have 46 chromosomes in 23 pairs and most great apes have 48 in 24 pairs. That leads to the prediction that two pairs of chromosomes merged in the human line.
Then it was found that human chromosome 2 has exactly the characteristics that would be expected from such s as merge and the genes on that chromosomes are those on two of the ape chromosomes. Furthermore, the placement of genes in the ape chromosomes lines up with the human chromosome if there was a merge. Finally, there is no reason for the human chromosome to have the characteristics it has unless it was a merge from two previous chromosomes in the past.
Now, if you object to the conclusion that the chromosomes merged and that shows a common ancestor with the other apes and humans, you need to explain these facts. In particular, you need to explain why human chromosome 2 has two centromeres and three telomeres when chromosomes usually have one centromere and two telomeres. You would also need to explain why the genes in the chromosomes line up as if there was a merger.