Ch 9 — Advances in Reproductive Biology and Their Effects on Animal Improvement *179 
rlu' itltMl tt‘clmi(|iu' li)i- making genetic (•t)|)ii*s 
of an\ atliilt mammal iinoKcs ins<M'tin^ 
tin* lUK'ltms from a hody roll (oof a sr\ rrll) f Vom 
an adult indi\ itlual into an o\ um. \rhir\ iof' this 
will prohahK takr yrars, if indrrd it is possihir 
at all. sinrr thrrr is somr r\ idrnrr that most 
atlulf l)(ul\ rolls arr iiTo\ tM'sihly dif trr(*ntialrd. ' 
Sri ioiis trrhniral hai rirrs must hr o\ t‘rromr 
hrf'orr acKanta^rs in animal produrtion ran h(‘ 
f'orrsrrn. 
eta. I, f i SION 
This ti‘rhnolo^\ fusrs two maturr o\ a or fri'- 
tilizrs onr o\um w ith anothrr. C'omhining o\a 
from ihr samr animal is ralird srlfin^. " I'lu* 
comhination of o\a has rrsulfrtl in \ rry rarly 
dr\ rlopnu*nt of tht' Iransfrrrrd rmhr\'o. hut no 
furthrr dr\ riopmrnt has h(>rn ia*poi trd. 
C!rll fusion trrhnolo^\ ma\ somrday pro\r 
usrful for transfrrrin^ firnotir matrrial fiom a 
somatir rrll into a frrtili/rd singir-ri'll rmhryo 
foi’ thr [)urposr of rioning. Sidfin^ would rapid- 
ly rrsull in purr grnrlir (inhi rd) linos for usr as 
brooding storks. I hi' trrhni(|ur rould also load 
to thr rapid idrntifiration of undrsii'ahlr rrrrs- 
si\r traits that rould hr eliminated from the 
species. 
CHIMtlK \S 
The produrtion of chimeras requires the fu- 
j, sion of two or more early emhr\os or the addi- 
Mn Jamuirv 1981 it was rt'portt'd that Ixxlv cells from a very 
early enthryo could act as donors of nuclei for cloned mice. 
tion of extra cells to blastocysts, fhese genetic 
compoiKMits may he from closely relatful Init dif- 
ferent sprci(*s. 
t,i\f‘ chimeras between two species of mouse 
ha\(' hr(Mi produced. tlowe\(M', practical appli- 
cations of chimera tc'chnology to li\ estock are 
not oh\ ious at this stage of tlex elopment. fhe 
main object i\e of this research is to provide a 
genetic tool for a better understanding of de\ el- 
opmiMit and mat(>rnal-fetal interactions. 
lU'COMHIV AN T l)N A AM) (JliNK TKANSFEH 
The nuH'hanics of diriH'tly manipulating the 
l)\.\ molecules of farm animals ha\e ivil yet 
lu'rn workful out. However, cells from mice 
ha\c luMMi mixed with pieces of chromosomal 
l).\ A, w hich became stably associated with the 
cells' own I).\.\. In addition, on September 3, 
19<S(), th(> successful introduction of foreign 
I)\ A into mouse embryos was announced. The 
embryos wei'r implanted into surrogate moth- 
ers who ga\e birth to mice containing altered 
D.VA. \\ hether or not the l)\V\ was active is un- 
known at this writing. 
Knowledge of the genetics of farm animals 
must improx e before rDN'A or other gene trans- 
fer methods will he of practical benefit in 
producing meat and lix estock products. Before 
genes can he altered they must he identified, 
and gene loci on chromosomes must be 
majiped. Work toxx ard this goal has begun only 
recently and rapid progress cannot be antici- 
pated. Multixariate genetic determinants of 
characteristics are anticipated to be the rule. 
Genetics and animal breeding 
I Txvo characteristics distinguish the reproduc- 
tion of farm animals from that of single-cell or- 
! ganisms: animal reproduction is sexual— male 
and female germ cells must be brought together 
to initiate pregnancy and produce offspring; 
and animal reproduction is sloxver (the genera- 
tion interx'al is longer), thus the economic bene- 
fits of specific gene lines may take years to be 
captured. These txvo characteristics limit the 
speed and extent to xvhich genetic improve- 
ments can be made. Reliable information about 
the genetic x alue of particular individuals is the 
key to overcoming limitations, for it can simpli- 
fy specific breeding decisions and spread desir- 
able genes throughout the Nations’s herds and 
flocks. 
The use of applied genetics for farm species is 
indirect. Breeders do not work with individual 
genes; rather, they must accept a genetic pack- 
