One more thing. You asked, "Is the removal of Rad51B, Rad51C, Rad51D, DMC1, XRCC2, or XRCC3 as lethal as the removal of both copies of Rad51 from a mammal?" Notice that the telic hypothesis I raised has led you to raise a question that could easily be turned into a testable hypothesis. In fact, since I started speculating along these lines, both TP and Nick came up with their own testable hypotheses that would address some point along the way.

Since Nick answered your question, let me add a couple more things. The seven versions are not always crucial. Baker's yeast, a stream-lined unicellular fungus, only has four versions. And fruit flies and mosquitoes are missing at least one of them.

Butt in any time you want. I think your long answer truly demonstrates what is great about the scientific community. You actually took a little of your time to help others learns how to gather information on their own. That was actually quite kind.

(Hopefully Mike won't mind me butting in…)

Short answer: yes, for many of those genes, complete loss is embryonic lethal.

Long answer:
FYI, you can find that info for those or any other genes that catch your interest at the Mouse Genome Informatics database

http://www.informatics.jax.org

Enter the gene name in the search box (select Gene symbols/names in the drop down menu). You'll find that most of the Rad51-family genes have different symbols in the mouse genome, but a search with the old symbol that Mike used will pull them up.

Click on the gene symbol to go to the detailed page. Scroll down to "Phenotypes" If the gene has been knocked out, one or more alleles will be listed for "targeted" Sometimes there'll be a brief summary of the phenotype on the main page. If not, you can click through to details of phenotype.