Tim writes:

>> There's been a great deal written on this subject here in the last week,
>but
>> not all of it was quite correct. In that regard, let me correct Tim's few
>> sentences.
>> 
>> Firstly, there is no recombination on the Y chromosome, thus there can be
>no
>> "gene swapping." Recombination occurs between sister
chromatids of two
>> homologous chromosomes, of which the Y has none. 
>
>[...]
>
>> Nevertheless, this mild form of error recovery isn't possible on a single
>> unpaired chromosome, absent of a homolog. Nor is such gene swapping 
>> possible on a palindromically encoded gene sequence, at least to the 
>> best of anyone's knowledge. [...]
>
>To make sure we are on the same page here...
>
>This thread arose from a pointer to:
>
>  http://www.genome.gov/11007628
>
>This says:
>
>``Instead, the Y appears to exchange genes between the two copies of 
>  repeated sequences that lie near to each other as mirror images.''
>
>...and...
>
>``The extensive use of gene conversion appears to play a role in the 
>  ability of the Y chromosome to edit out genetic mistakes and maintain 
>  the integrity of the relatively few genes it carries.''
>
>...which seems to directly contradict the things that you are saying.
>
>Are you saying this study is completely mistaken?

No, not completely, but their few sentences are misinformative. "Gene
conversion" is a mismatch repair mechanism. The general description of the
process of gene conversion is that it's a 50/50, flip-of-the-coin process. A
new match in base pairs will be accomplished, but it's only a 50/50 chance that
the code will be restored back to its original form, which is simply another
way of saying what I wrote earlier. Please see the first few paragraphs in:

   http://www.blc.arizona.edu/marty/411/Modules/genconv.html

Gene conversion is a "repair" mechanism only in that it restores the the
palindrome but it does not guarantee that the informational integrity of the
original content will be maintained. The sentence you quoted, "The extensive
use of gene conversion appears to play a role in the ability of the Y
chromosome to edit out genetic mistakes and maintain the integrity of the
relatively few genes it carries," is fundamentally in error.

Wirt Atmar
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