Passing on mutations?

[JHolliday]

I can't find this anywhere. The idea of passing on mutations solely through germ cells is not really explained well in any class I've had, or text I've read. I also can't find it on the internet.

What is the average rate of mutations in a single germ cell? This information is really crucial in calculating the feasibility of the production of the genetic diversity we see around us today. I've seen numbers on the mutations someone would obtain over the coarse of their lifetime, but I think this for somatic and germ cells.

To know how much genetic diversity could be created over a given amount of time. You need to know how the mutation rate for a germ cell. Does anyone know what this is?

[JackBean]

Why should be it different in stem cells and in germ line cells?

[Dougalbod]

There are probably different estimates and ways of calculating this, but here is one figure.....

Average mammalian genome mutation rate is 2.2 × 10−9 per base pair per year ("Mutation rates in mammalian genomes", Kumar, Subramanian, PNAS January 22, 2002 vol. 99 no. 2 803-808. http://www.pnas.org/content/99/2/803.full)

I think that there is evidence that mutation rates in germ cells are lower than in somatic cells, but I don't have a reference. It does seem to have some logic that an organism willput more energy into managing mutation rates in germ cells though....

Dougal

[kolean]

I would like to add some info about germ cells. Germ cells have meiosis (as oppose to just mitosis in somatic cells), in which there is crossing over/meiotic recombination. This extra mechanism could potentially have a higher mutation rate.

But, on the other hand, the organism's epigenetics has come up with methylation of DNA (and possibly the methylations, acetylations, well any modification of histone tails that also silences genetic DNA and regulatory DNA) to counteract the threat of mutations.

[JackBean]

how can the histone modifications threat mutations?

[zami'87.]

@kolean
There's mitotic crossing over also,although it's rare.
http://www.ncbi.nlm.nih.gov/bookshelf/b ... &part=A683
Effective repair system lowers mutation rate..xeroderma pigmentosum,ataxia telangiectasia and many other disorders have deffective repair system
@JackBean
Maybe because histone modifications affect on condensation/decondensation and thus prevent/enable DNA binding and expression of genes

[JackBean]

I thought, that mutations arise during replication, not transcription...

(of course there too, but that has no influence)

[zami'87.]

I thought, that mutations arise during replication, not transcription...

(of course there too, but that has no influence)

yes they do..but here I guessed that prevention of expression of mutated gene (and changed function/or degradation time of it's (sometimes dominant) product) can in some cases mild effects.
But so far I haven't found an example in textbooks..so it's guessing

[kolean]

"These abnormal chromatin states may lead to
genomic instability, enhanced mutations rates, loss of imprinting,
oncogene overexpression or silencing of tumor suppressor genes"
from an article (not on germ cells, but I imply)

http://www.ncbi.nlm.nih.gov/pubmed/1848 ... &linkpos=3

I was mostly centered on the suppression of transposable elements due to DNA methylation, and its possible histone methylations, that is found in germ cells, to keep mutations from transposable elements suppressed.