# Percent Recombination – Gene Mapping

by Georgina Cornwall, PhD
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00:00 see evidence of it in the phenotype. When we think about doing a genetic map, we know that we have all of our linkage groups, each chromosome. So humans, we have 23 different linkage groups of 46 chromosomes because they come in pairs. We can obtain linkage data based on crosses and this was done a lot in fruit flies in order to perfect the technique of genetic mapping. You have to keep in mind that genetic mapping is relative distance based on these recombination frequencies. Nothing is actually being measured. We are going to look at the percent recombination to give us an estimate of the distance apart two genes are on a chromosome. Here is an example of looking at those crossing over events, we might see those crossing over, we can draw them as simple lines. I like to do that to keep track of things while I am calculating recombination frequencies and we call these units, these percent recombination either a map unit or a centimorgan. Let us say we run into 30 percent recombination, we can say it is 30 centimorgans from the other allele or we could say that it is 30 map units. Those things are exactly the same, measurement.

The lecture Percent Recombination – Gene Mapping by Georgina Cornwall, PhD is from the course Understanding Genetics.

### Included Quiz Questions

1. …the relative distance between two genes on the same chromosome based on the recombination frequency.
2. …the actual distance between two genes on the same chromosome based on the number of nitrogenous bases present in between them.
3. …the relative distance between two genes on the different chromosomes based on the recombination frequency.
4. …the actual distance between two genes on the different chromosome based on the number of other genes present in between them.
5. …the actual distance between two genes on the different chromosome based on the number of nitrogenous bases present in between them.

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