Question #ab245

1 Answer
Jan 8, 2018

The frequency of crossing over is proportionate to the distance between linked genes.
When linked genes are far apart on the same chromosome, the frequency of crossing over increases.

Explanation:

Genes on the same chromosome are "linked."

It would be expected that linked genes would be inherited together because the gamete gets each chromosome as an entire piece.

But that is not what happens.

Instead, during meiosis, small sections of homologous chromosome might switch places with each other, each ending up on the other chromosome.

This is called "crossing over."

Crossing over separates two linked genes more often if the genes are far apart from each other.

But if two linked genes are close to each other, the chance is less that any break will randomly happen right between them and separate them.

Here is an image of the relative frequency of crossing over

enter image source here
http://www.biologyreference.com/La-Ma/Linkage-and-Gene-Mapping.html

Linkage and crossing over frequency were greatly important in gene mapping.

Geneticists were able to map the location of genes by how often they cross over. The more often, the further apart any two linked genes must be.

Here's a Khan Academy video that you can view to see more information about linkage, crossing over, and gene mapping: