I'm used to seeing genetic drift measured in centimorgan units. The presence of the "centi" prefix implies there is a morgan unit equal to 100 centimorgan.

However, looking at lists showing the centimorgan scale, there appears to be nothing special about 100 centimorgans.

What is a morgan?


Putting "centimorgan definition" into a search engine brought this up (first hit):

Centimorgan is named after an American geneticist named Thomas Hunt Morgan. He worked on fruit flies, and he defined the capacity of one part of a genome to separate from another in going from one generation to another. And that's important because in every generation chromosomes exchange pieces of information, and that's call recombination. And that's important for introducing genetic diversity into the population. And it was necessary to define a rate at which this happens, and so that's where this term centimorgan comes from. "Centi" means just one-hundredth of, and so if a "morgan" represents the total recombination where all markers of one part of a chromosome will become separated from all others, then a centimorgan is the length of DNA over which that happens only one out of a hundred times, or one percent of the time. So one percent recombination equals a centimorgan. It depends on individual genomes what the distance that a centimorgan represents, and in individual genomes is different from fruit flies and zebrafish and bananas and humans, but given the recombination rate in humans, it represents about a million base pairs in the human genome.

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