Expanding genomes?

[nativecoder]

Hi all,

I have some dumb questions about insertions/deletions

 

A) What is more common (regarding the changes in the genome), insertions or deletions?

 

B) What is more common (insertions or deletions) regarding the genome area (introns vs exons)?

 

C) If insertions are more common, then the genomes are in a continuous expansion (that in the end means more junk DNA nature has to play with). Is there any lab method (I mean physical method) to measure the potential length of the genome of an organism before sequencing? (no idea, maybe weighting the chromosomes?)

[CharonY]

There are generally more mechanisms around (e.g. mobile genetic elements) that increase the size of the genome, though depending on the organism not everything ends up in the chromosomes. It also depends on the genomic area. Highly conserved areas which cover essential functions rarely get changed. Or more precisely, if something happens there it may lead to a reduction in fitness and as such it is not stable over generations.

And that is the second thing you should keep track of, while thinking about it: stability. Something might get inserted in the genome, but if it is not in a germ cell, it will get lost. If it is in germ cell it may get lost if it reduces fitness to the carrier, regardless whether there are insertions or deletions. It also depends on the organisms. For small ones, like bacteria an insertion has a larger cost associated with it (the relative energy required to synthesize the additional bit of DNA) than for a very large one. So there is selective pressure to maintain a small genome, unless the new bit increases fitness. Then those that lost it will be selected against.

 

For measuring genome size there are a number of techniques out there. The easiest is probably pulseö-field gel electrophoresis, but restriction maps are a bit more accurate.

[Mokele]

Flying animals also have reduced genome size, compared to their non-flying relatives, possibly due to either the metabolic cost of copying large amounts of DNA, or due to correlated changes in cell size and effects of metabolism.

[CharonY]

This is fascinating, Mokele I wonder whether there are large scale genomic studies around.

[nativecoder]

very useful!

Many thanks.