MathBench > Probability

Linked Genes and Recombination
Advanced Punnett

Fun with map units...

The rate of crossover depends on a lot of things like species, gender, age, and so on, but most importantly (for our purposes), it depends on distance between the genes.

This concept is so important that geneticists talk about distance in "map units", where 1 map unit = 1% probability of crossing over.

sudoku with smiley facesBy the way, what is the maximum rate of crossover? You might be tempted to say "100%" (I know I am). However, talking about a 100% crossover rate doesn't really make sense. In fact, at a crossover rate of 50% or more, you can't tell the difference between linked genes and unlinked genes. So the highest crossover rate that makes sense is 50%, or 50 map units.

If you like Sudoku, you'll love map units. Give them a try:

Start with B and C, since they are the farthest apart A and B 10 units apart
A has to be BETWEEN B and C, so this is the only place it can go, 7 map units from C. CAB or ACB
Just to verify, A is also 10 map units from B. CAB is the only answer that works

Here are a couple more:

  • P and T --> 11%,
  • T and O --> 10%
  • P and O --> 1%

This one is a lot harder!


  • U and N --> 5%,
  • G and S --> 33%
  • U and S --> 21%
  • N and G --> 7%