Behavioral Genetics and Animal Science - Genetics and the Behavior of Domestic Animals - page 30

“picture center” in a television set was found after cutting one circuit inside
the set used to create the pictures. Gerlai (1996) and Crawley (1996) also
warn that knocking out the same gene in two different species may have
different effects on behavior. This is due to the complex interactions between
many different genes.
Thirty-five years ago behavior geneticists found that inheritance of
behavior is complex. Fuller and Thompson (1978) concluded, “It has been
found repeatedly that no one genetic mechanism accounts exclusively for a
particular kind of behavior.”
Transgenic Mice
Since the first edition of this topic was published, hundreds of papers have
been published on mouse models of conditions such as autism and various
behavioral extremes ( Roullet and Crawley, 2011 ; Silverman et al., 2010 ).
Models of high-novelty-seeking mice, timid mice, fearful mice, and obsessive-
compulsive mice are used to study these conditions in humans ( Lipkind et al.,
2004 ). There are different behavioral tests for the hundreds of types of spe-
cial mice. Crawley (2007, 2008) devoted an entire topic to behavioral testing
of transgenic mice. Eisener-Dorman et al. (2009) stated that knock out
procedures do not always work correctly to produce the desired effects and
is concerned that transgenic mice are not always what they were originally
bred to be.
Random Factors
Behavioral geneticists find it impossible to completely control variation in
some traits. Gartner (1990) found that breeding genetically similar inbred
lines of rats failed to stop weight fluctuations. Even under highly standard-
ized laboratory conditions, body weights continued to fluctuate between ani-
mals. Pig breeders also observe that commercially bred hybrid lines of pigs
do not gain weight at the same rate. Even in genetically identical animals,
random unknown factors affect variability. In utero factors may be one
cause, other causes are unknown. Dr Daryl Tatum and students at Colorado
State University found both body conformation and meat quality variation
in 50% English (Bos taurus) and 50% Brahman (Bos indicus) cattle. Some
animals showed more Brahman characteristics, with larger humps and longer
ears. However, the body conformation was not half English and half
Brahman, and meat characteristics varied as well. Cattle that looked more
Brahman had tougher meat. The animals had about 10% variation from the
body shape and meat characteristics of Brahman half-bloods.
Gartner (1990) concluded that up to 90% of the cause of random variabil-
ity cannot be explained by differences in the physical environment. In both
mice and cattle, random factors affected body weights. Gartner (1990)