[Jacob-list] Jacob genetics vs. environment

[Anderson, Gary B.]

Recent Jacob List discussion touched on what's inherited and what's not in
Jacob sheep.  Perhaps we will learn a bit more about the subject over the
next few months by measuring similarities and differences in identical
twins.  The idea sprang from a question by Fred Horak on what, if anything,
is known about characteristics of identical twin Jacob sheep.  I didn't have
an answer to the question and didn't even know whether identical twin Jacob
lambs ever had been documented.  But production of identical twins by
embryo-splitting techniques is a reasonably successful research tool, and
with the volunteer help of graduate students and technicians in my lab I
(and of Dianne Anderson and Robin Lynde who gave up a day to help with
embryo transfer surgeries) we conducted a small experiment aimed at
producing identical twin Jacob lambs.  Briefly, we collected embryos from
Jacob ewes at 5-6 days after breeding.  The embryos have 100+ cells at this
stage and can be split under a microscope into half-embryos each having 50
or so cells.  When put back into the reproductive tract of a ewe,
half-embryos have a reasonably high survival; on average survival of each
half-embryo is only slightly lower than that of the original intact embryo.
Last September we transferred 22 Jacob half-embryos (i.e., 11 split embryos)
to the reproductive tracts of eight Polypay ewes.  Seven ewes maintained the
pregnancy and delivered 12 lambs, including four sets of identical twins (2
male sets and 2 female sets).  Unfortunately, one lamb of a male set died
during delivery, leaving three living, intact twin sets.  Color patterns on
identical twins are more similar than I expected, based on previous
embryo-splitting results with, for example, Holstein cattle.  The twins show
some interesting differences; for example, one lamb has a knee spot on only
its left foreleg, and the identical twin has a knee spot on only its right
foreleg.  A characteristic of interest will be horn placement in four-horned
sheep.  When the twins are a bit older (they're a month old as we speak) and
we have additional observations, I intend to summarize the results for
publication.  One gigantic caution is that our results will be purely
descriptive, as three identical twin sets are too few to draw major
conclusions.  If these twin sets produce interesting results, perhaps we can
undertake another experiment next fall to increase the number of identical
sets for study.  For now, the project has been an interesting one stimulated
by the Jacob List, and I thank Fred Horak for asking the question that
prodded me to do the experiment.