Genetic Distance Between Genes On Different Chromosomes

Question

[Spandankeshav]

If two genes are in different chromosomes then how can we measure the distances between them?

[Pierre Lindenbaum]

What do you mean with '''distance''' ? a recombinant frequency (cM ) ?

[David Quigley]

He could mean the physical distance (measured in micrometers or some suitably small unit). That would vary over the life of the cell.

[David Quigley]

He could mean physical distance, e.g. measured in microns rather than base pairs. That would vary over the life of the cell.

[Spandankeshav]

Yeah Pierre you are right. I mean recombinant frequency (cM).

[Giovanni M Dall'Olio]

changed the title. Come on, try to think of a better title when posting here.

Answer 1

[Casey Bergman]

The "recombination" frequency of two independent linkage groups (chromosomes) is defined as 0.5 because of Mendel's Second Law of Independent Assortment.

From wikipedia: "any alleles that are completely unlinked (e.g. alleles on separate chromosomes) have a 50% chance of recombination, due to independent assortment."

A recombination frequency of 0.5 implies two genes are "unlinked," regardless of whether they are on the same or different chromosomes.

Answer 2

[Giovanni M Dall'Olio]

You calculate it in the same way as you do for genes on the same chromosome. If two genes are in linkage disequilibrium even in this condition, it may mean that they are involved in the same function. Note that you don't need to know whether two genes are on the same chromosome to calculate their genetic distance; in fact, Morgan's student Sturtevant did not even know the concept of chromosome when he coined the definition.

[Sudeep]

"If two genes are in linkage disequilibrium even in this condition, it may mean that they are involved in the same function" could you please cite the source from where you got this information ? just for reading up

[Giovanni M Dall'Olio]

it just comes from the definition of Linkage Disequilibrium http://en.wikipedia.org/wiki/Linkage_disequilibrium . If two alleles of different genes on different chromosomes tend to be inherited together with a frequency different that what expected, it may be because they are associate with the same function and having the two alleles together gives some sort of positive advantage to the individuals. Of course, it may simply be the result of drift or hitch-hiking.

Answer 3

[Pierre Lindenbaum]

aside from the Chromosomal abnormalities there is no recombination/crossing over between two non-homologous chromosomes, so the genetic distance has no meaning here.

[Giovanni M Dall'Olio]

it makes sense to calculate genetic distance between genes on different chromosomes, because if two genes are in linkage disequilibrium even in this condition, it may mean that they are involved in the same function.

[Pierre Lindenbaum]

thanks for the clarification Giovanni