New Advances in Cloning and Their
Potential Impact on Genetic Variation in Livestock by JA Woolliams, I Wilmut
Journal of Animal Science. 68:1357-7298;
March, 1999
Abstract: Cloning has advanced through the recent
demonstrations that it is feasible to produce, in principle and with
significant effort, an unlimited number of individuals of identical genotype
from differentiated cell lines that have been frozen and thawed. These
advances have been based upon understanding the importance of interactions
between the stage of the cell cycle of both the oocyte and donor cell for
the success of the nuclear transfer. Whilst the impact of the biological
advance is immense for biomedical applications, the significance is less
clear for livestock breeding. In our view the scientific issues for breeding
programmes lie in whether clones can increase genetic progress without
a cost to biodiversity. Biodiversity within a species may be categorized
as: (i) between-breed variation; (ii) genetic variation among parents
within breeds; (iiii) genetic variation among individuals within a farm;
and (iv) allelic variation within an individual. In the face of a vapid
global decline in breed diversity, cloning, in particular cloning of adults,
may be an important route to protect biodiversity since it may allow far
more genetic variation to be made available for new breed development in
the future than is practicable at present. For variation among parents,
the judicious use of clones may give significantly faster rates of progress
without increasing the rate of loss of genetic variation and furthermore
can help improve traits associated with health and welfare which are at
present less tractable than, say, milk yield. Local diversity within a
farm may be greatly affected if cloning is utilized to disseminate genetic
progress widely and more answers are required on the importance of genetic
variation within any one locality either in buffering diseases or ameliorating
other management problems. Experience from clonal forestry can provide
some indications but now there are models capable of answering this question
directly in livestock. Allelic variation within individuals per se is not
generally advantageous but at loci where it is identified to be beneficial,
the use of cloning may exploit it more widely.
