[nonbel]

See my other post here. They don't report the initial number of zygotes injected (why not?) so we cannot assess the "selection" explanation.

They got 11 surviving mice in the end, but only 7 were "edited", and usually we see that ~1%-.1% cells are mutants at any given site I would expect they needed ~ 1000 zygotes.

This only really explains the NHEJ results though, not the HDR (when the repaired DNA includes an exogenous template). They report that 2 (out of the 7) mice had the sequence matching the template. However this was only in some of their cells (36% and 19%).

Two other mice had a sequence that was similar but contained mutations...

Anyway, maybe someone can email them and ask how many zygotes were used originally.

[nonbel]

It looks like this strain of mice can produce ~10 pups (a lower bound since not all zygotes will make it to birth) every 5 days for 26 cycles. So, one breeding pair could produce at least ~260 zygotes in 4 months. From this, I'd say it is plausible (economically) that the number of zygotes injected for this study was in the thousands:

>"The fecundity of the FVB/N strain was assessed by data from nine breeding pairs, which produced 43 litters. Litter size ranged from 7 to 13, with a mean value of 9.5. (First litters were generally smaller.) This is superior to other commonly used inbred strains; for example 6.7 for C57BL/6J, 6.6 for SJL/J, 5.4 for 129/J, or 5.0 for DBA/2J (15). A typical breeding pair mated at every postpartum estrous cycle and continued breeding for at least half a year, usually longer." http://www.pnas.org/content/88/6/2065.full.pdf

>"Mice have a 4-5 day estrous cycle and ovulate on the third day. Placing the females with a male on the third day of their cycle will result in the maximum number of pregnancies." Also from the same reference (table 1), number of fertile cycles is ~26: https://www.jax.org/strain/001800