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l-bow · 02-04-2002, 04:25 AM

In another thread davidH mention the mutation rate was 1 to 30 per 1,000,000 gametes. That's strange. I have read that the average number of mutations per gamete is about 5. What number am I to believe? scigirl? DNAUnion? anyone?

[ February 04, 2002: Message edited by: l-bow ]</p>

Peez · 02-05-2002, 07:40 AM

The rate that davidH mentioned sounds more like mutations per gamete in a specific gene. For example, a mutation in a specific gene causes retinoblastinoma. This particular mutation occurs 1.2-2.3 times in 100,000 gametes (Dobzhansky, 1970, as quoted in Futuyma, 1998). However, there are tens of thousands of genes. A collegue of mine who does research on DNA repair mechanisms estimates that each human has (on average) about five brand new, phenotypically-detectable mutations.

Peez

theyeti · 02-05-2002, 07:55 AM

This is slightly related, but interesting none the less. Any of you who are biologically inclined (and mathematically -- sheesh!) should read <a href="http://www.pnas.org/cgi/content/full/99/2/803" target="_blank">Mutation rates in mammalian genomes </a> Proc. Natl. Acad. Sci. USA, Vol. 99, Issue 2, 803-808, January 22, 2002.

Quote:

Similarity of mutation rates among lineages with vastly different generation lengths and physiological attributes points to a much greater contribution of replication-independent mutational processes to the overall mutation rate. Our results suggest that the average mammalian genome mutation rate is 2.2 � 10^-9 per base pair per year, which provides further opportunities for estimating species and population divergence times by using molecular clocks.

If you multiply that rate times the 3.2 x 10^9 base pairs in the human genome, that comes out to 7.104 mutations per year. I don't know how to translate that for a given gamete, but either way it's relatively high. Here's some other interesting tid bits:

Quote:

We examined the temporal constancy of neutral evolutionary rate among diverse mammalian lineages. The divergence time and evolutionary distance for 43 mammalian pairs clearly show a linear relationship (correlation coefficient = 0.97) with the regression analysis indicating that the mammalian genomes accumulate mutations at an average rate of 2.22 � 109 substitutions per site per year (Fig. 5a). We also estimated the mutation rate by using only fossil-based divergence times for intraordinal splits and 90 million years for superordinal divergences (29-31). This yields an upper bound of 2.61 � 109 substitutions per site per year (Fig. 5b).

Fig. 5. Accumulation of neutral substitutions over time (million years) in diverse mammalian species. The average distance per lineage is plotted for inter- and intraordinal comparisons by using, respectievely, molecular data-based (a) and fossil-based (b) time estimates reported previously. Linear regression produced a rate of 2.22 � 109 substitutions per site per year million years ago (r = 0.97, n = 43) for the molecular data and 2.61 � 109 substitutions per site per year (r = 0.92, n = 33) for the fossil data.

In case you missed it, the point here (or at least my point) is that the predicted genetic distance based on divergence time from the fossil record matches with that seen from molecular data. This is very strong conscilience of data that points to evolution.

This is also interesting:

Quote:

However, the relationship of the number of germ-line cell divisions and the mutation rate clearly is not linear as is indicated in the difference in the ratio of the male/female mutation rate in primates and rodents. Primates show a male/female mutation-rate ratio (37, 38) that is almost the same as seen in rodents even when the ratio of the number of germ-cell divisions in males and females is almost 3-fold higher in humans as compared with mice. Therefore, our results suggest that replication-independent mutational processes (e.g., DNA methylation, recombination, and repair mechanism) may play a greater role as a source of mutation than that anticipated earlier (4, 38, 39).[my emphasis]

In conclusion, our results argue against the widely held notion about large differences in mutation rates among genes in a genome and among major mammalian lineages. This approximate similarity of mutation rates among genes and among lineages is likely to be important for estimating divergence time for closely related species, testing for selection by comparative sequence analysis, inferring coalescent times, and understanding the mutational processes that govern evolution of mammalian genomes.

It looks like the molecular clocks are back in action, at least for mammals.

theyeti

{edited to add an important minus sign}

[ February 05, 2002: Message edited by: theyeti ]</p>

02-04-2002, 04:25 AM	#1
l-bow Regular Member Join Date: Jul 2001 Location: Hawaii Posts: 215	mutation rate for a given gamete? In another thread davidH mention the mutation rate was 1 to 30 per 1,000,000 gametes. That's strange. I have read that the average number of mutations per gamete is about 5. What number am I to believe? scigirl? DNAUnion? anyone? [ February 04, 2002: Message edited by: l-bow ]</p>

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02-05-2002, 07:40 AM	#2
Peez Veteran Member Join Date: Apr 2001 Location: Canada Posts: 5,504	The rate that davidH mentioned sounds more like mutations per gamete in a specific gene. For example, a mutation in a specific gene causes retinoblastinoma. This particular mutation occurs 1.2-2.3 times in 100,000 gametes (Dobzhansky, 1970, as quoted in Futuyma, 1998). However, there are tens of thousands of genes. A collegue of mine who does research on DNA repair mechanisms estimates that each human has (on average) about five brand new, phenotypically-detectable mutations. Peez

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