Chicken Genome
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Elucidation of the chicken genome has wide-ranging implications for agriculture
and biology. Genetic mapping in chickens has a long history. The recent use
of DNA markers has allowed the construction of a consensus genetic map
containing 51 linkage groups. Chickens have 39 pairs of chromosomes including
microchromosomes. Thirty-two of the linkage groups have now been assigned to
speciFc chromosomes using fluorescence
in situ
hybridization to reveal the location
of speciFc genes on the cytogenetic map. A detailed BAC map of the entire chicken
genome is being assembled and will be merged with a whole genome shotgun
sequence. The comprehensive collection of chicken expressed sequence tag ESTs
will be indispensable for annotating the physical map of the genome. The chicken
genome is particularly well placed in the evolutionary tree to provide new insights
into vertebrate gene and genome evolution during the past 300 million years.
1
Importance of Chicken Genomics
Chicken genomics have wide-ranging ap-
plications because the chicken is important
both from agricultural and biological view-
points. Chickens are arguably the most im-
portant source of animal protein for the hu-
man population worldwide. The chicken is
also the most widely studied avian species
and as such provides a warm-blooded ver-
tebrate model. Their relative cheapness
and high reproductive rate make them rel-
atively accessible for genetic approaches.
±urthermore, because there are both sim-
ilarities and differences between chickens
and humans, genetic comparisons should
be particularly illuminating.
±rom the agricultural viewpoint, the
main issues have been to do with features
such as growth, meat quality, and egg pro-
duction, and breeding programs have been
selected for these different traits leading to
broiler (meat-type) and layer strains. More
recently, other traits such as the genetic
basis of disease susceptibility and those
associated with behavior are coming to the
fore. Chickens provide excellent models
for investigating quantitative trait loci for
these and other parameters that may also
be relevant to mammals and even humans.
A surprising number of fundamental
biological discoveries have been made in
chickens in areas as far apart as virology,
immunology, and developmental biology.
It was in chickens, for example, that it was
Frst discovered that viruses could cause
tumors and that B cells are a distinct class
of lymphocytes. The immune system of
chickens differs from that of mammals
in that antibody diversiFcation is based on
the high frequency of gene conversion that
occurs at immunoglobulin genes rather
than on combinatorial joining, and this
provides a novel perspective.
Because of the high frequency of gene
conversion at chicken immunoglobulin
genes, a chicken cell line, DT40, de-
rived from a chicken bursal lymphoma
has proved to be a powerful tool for as-
sessing the function of genes that act
cell-autonomously. Homologous recombi-
nation between host genomic and trans-
fected DNA in DT40 cells is as efFcient
as in budding yeast. These cells have been
used to probe gene function in several
cell biological processes, not only in anti-
body diversiFcation but also, for example,
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