Biology Reference
In-Depth Information
chickens, and dogs amongst others ( Chen et al., 2009; Clop et al., 2012;
Fadista et al., 2008; Liu et al., 2010; Wang et al., 2010 ).
The effects of CNVs can be extremely varied, as can their mechanisms.
Confining ourselves to domestic animals ( Clop et al., 2012 ), effects have been
found on color in horses (premature graying ( Rosengren Pielberg et al., 2008 )),
goats ( Fontanesi et al., 2009 ), and sheep ( Norris and Whan, 2008 )(bothwitha
CNV in the ASIP gene), morphology in chickens (causing the classic pea comb
variant ( Wright et al., 2009 )), and also late feathering in the same species
( Elferink et al., 2008 ). In dogs CNVs are related to the ridge mutation in
ridgeback dogs ( Salmon Hillbertz et al., 2007 ) and chondrodysplasia in a vari-
ety of small dog breeds ( Parker et al., 2009 ). These examples are all discrete
mutations. However one study did find an association between production
traits and CNVs in cattle ( Seroussi et al., 2010 ), though in this case the exact
mechanism has not been conclusively proven.
Moving away from domestic animals, other examples of correlations
between complex diseases and CNVs have been identified ( Stankiewicz and
Lupski, 2010; Zhang et al., 2009 ). Associations with neurocognitive defects
( Brunetti-Pierri et al., 2008; Golzio et al., 2012 ), autism ( Sanders et al., 2011 ),
and schizophrenia ( Sebat et al., 2007 ) are of particular note in a behavioral
setting. The actual mechanisms by which CNVs affect the expression of a trait
can be extremely varied and range from the simple to the complex. At the most
basic level, deletions (a form of CNV) can remove one or more exons from one
or more genes (or indeed even entire genes), leading to large changes in the pro-
tein that is expressed. More subtly, dosage effects can be found, with the greater
the number of copies of a gene, the greater the expression (especially if the
gene promoter is also duplicated). Further mechanisms can be more complex
still, with transcriptional sites that up- or down-regulate a gene altered through
dissociation between these sites and their promoters, alteration of chromatin
structure and the like (see Henrichsen et al.(2009) for a brief overview), though
little is yet known about such regulation.
MAPPING GENES FOR BEHAVIOR—TOP DOWN APPROACHES
The mapping of genes for behavior is similar to mapping other quantitative
traits, only with the exception that the trait is often harder to define and measure
reliably. The general methods either use a top down or a bottom up approach.
Essentially this refers to whether one starts at the phenotype and attempts to
work down to the gene level, or whether one starts at a gene level and attempts
to work up to the phenotype ( Boake et al., 2002 ).
Pedigree Studies and Heritability Analysis
Initially this uses statistical analysis of pedigrees to demonstrate an actual
heritable component to the trait of interest, through breeding designs, artificial
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