Behavioral Genetics and Animal Domestication - Genetics and the Behavior of Domestic Animals - page 46

traits, Albert et al. (2009, 2011) did not find any evidence of a major,
domestication gene. Rather, genetic architecture and the combined effects of
several physically linked genes may explain the correlated selection
responses.
In a very similar study, focusing on Red Junglefowl (ancestors of all
domestic chickens), Agnvall and colleagues measured correlated behavior
responses to selection for increased tameness against humans over three
generations ( Agnvall et al., 2012 ). They found a moderate but significant
heritability for reduced fear of humans (h 2

0.17), and also significant
genetic correlations between fear of humans and, for example, foraging and
exploration, and hatch weight. This indicates that selection for tameness
is likely to cause correlated behavioral effects also in chickens, and again
suggests that genetic architecture of few and pleiotropic genes may control a
large part of the domesticated phenotype.
What is interesting in the study of the genetic architecture of domestica-
tion is that when these differentially selected, or indeed wild and domestic,
populations are then inter-crossed, these trait correlations begin to erode
( Albert et al., 2009; Wright et al., 2010, 2012 ). The implications of this are
discussed in the section on genetic architecture, below.

5

GENETIC MECHANISMS IN DOMESTICATION
All the standard genetic mechanisms that act on natural populations will also
act on domestic populations, though some to a much greater and others to
a much lesser degree. Genetic mechanisms affecting gene frequency can be
largely broken down in to systematic processes and dispersive processes
( Falconer and Mackay, 1996 ).
Systematic processes affect gene frequency in both a predictable manner and
direction, and include migration, mutation, and selection. Dispersive processes
have greater effects in smaller populations, and are often unpredictable in their
effects on populations. This is principally drift, but also inbreeding and assorta-
tive mating can fall under this category. In terms of the latter two (inbreeding
and assortative mating) these affect not only gene frequencies, but more
importantly genotype frequencies, as discussed below. Of these processes,
selection, inbreeding, and drift are perhaps the factors with the greatest effect
on domestic populations ( Price and King, 1968 ). Migration (i.e. new gene
flow into the population) is generally extremely tightly controlled in domestic
animals, whilst mutation may provide some novel discrete Mendelian (single
gene) phenotypes that are then selected upon. Quantitative traits will once
again be relatively unaffected in the relatively short time frame (evolution-
arily) of domestication (especially when one considers that some of the largest
changes in phenotype have occurred in the most recent selection history
of domestication). Assortative mating (whereby phenotypically similar
animals mate/are mated with one another) will have an effect in domestic