# What is the conversion ratio between centimorgans and recombination frequency?

Apr 9, 2019

## What is the conversion ratio between centimorgans and recombination frequency?

One cM is about 100,000 base pairs on a physical map and corresponds to 1% recombination during meiosis. This means that one crossing-over event between two loci that are one cM apart occurs in every hundred meioses.

## How do you calculate recombination fractions?

Divide the number of recombinant offspring by the sum of the recombinant and nonrecombinant offspring. In this example, dividing 40 by 100 gives 0.4. This is the recombinant fraction.

How do you convert to centimorgans?

To convert the percentage into centimorgans, just multiply your percentage by 68 (that will at least get you close). You can also see total shared cMs in the chromosome browser tool (go to Tools > DNA Relatives > DNA).

### How do you calculate recombination frequency?

Recombination frequency = # recombinants/total progeny x 100. Experimental recombination frequencies between two genes are never greater than 50%.

### How many base pairs are in 1 cM?

1 million base pairs
In humans, 1 cM is equivalent, on average, to 1 million base pairs.

What can a recombination frequency of 50% indicate?

A recombinant frequency of 50 percent generally means that the genes are unlinked on separate chromosomes. The remainder of this chapter focuses mainly on linked genes and recombinants arising from crossing-over.

## How is the centimorgan unit used in genetic genealogy?

In genetic genealogy, a centiMorgan (cM) or map unit (m.u.) is a unit of recombinant frequency which is used to measure genetic distance. It is often used to imply distance along a chromosome, and takes into account how often recombination occurs in a region. A region with few cMs undergoes relatively less recombination.

## How many base pairs does a centimorgan correspond to?

The number of base pairs to which it corresponds varies widely across the genome (different regions of a chromosome have different propensities towards crossover). One centiMorgan corresponds to about 1 million base pairs in humans on average.

Why is the number 6770 in centimorgan ISOGG?

A half-identical match (such as a parent/child) is 3385 cM. This number has to be doubled to represent both the maternal and paternal sides giving a total of 6770 cM. Matt Dexter explains: “The reason the number is not 6770 or 6800, but rather 68, is that it saves an additional step doing the math to convert an answer to percent.

### How are centimorgans related to distance and distance?

Centimorgans also depend on the cross involved and a large inversion can prevent recombination so large regions can be 0 centimorgans long in one cross, but many centimorgans long in another cross. My metaphor is centimorgans events correlated to distance but not related at the same ratio.