Principles of Plant Genetics and Breeding

Inducer
removes
inhibitor
Gene a
Inhibitor
which scientists genetically engineer organisms is by
manipulating the gene expression.
Synteny and plant breeding
In Chapter 2, Vavilov’s law of homologous series was
introduced. Gene order in chromosomes is conserved
over wide evolutionary distances. In some comparative
studies, scientists discovered that large segments of
chromosomes, or even entire chromosomes in some
cases, had the same order of genes. However, the spacing
between the mapped genes was not always proportional.
The term colinearity is used to refer to the
conservation of the gene order within a chromosomal
PLANT CELLULAR ORGANIZATION AND GENETIC STRUCTURE 53
DNA
mRNA mRNA
+
Protein a
(a) (b)
Gene a
Protein a
Activator
Figure 3.20 Schematic representation of the regulation of gene expression showing (a) negative gene regulation and
(b) positive gene regulation.
Clark, A.G. 2002. Limits to the prediction of phenotypes from
knowledge of genotypes. Evol. Biol. 32:205–224.
Crick, F.H.C. 1962. The genetic code. Sci. Am. 207:66–77.
Felsenfeld, G. 1985. DNA. Sci. Am. 253:58–78.
Holland, J.B. 2001. Epistasis and plant breeding. Plant Breed.
Rev. 21:27–92.
DNA
References and suggested reading
segment between different species. The term synteny is
technically used to refer to the presence of two or more
loci on the same chromosome that may or may not be
linked. Modern definition of the term has been broadened
to include the homoeology (homoeologous chromosomes
are located in different species or in different
genomes in polyploid species and originate from a common
ancestral chromosomes) of originally completely
homologous chromosomes. Whole-genome comparative
maps have been developed for many species, but are
most advanced in the Gramineae family (Poaceae).
Some researchers have attempted to clone a gene in one
plant species based on the detailed and sequence information
(microsynteny) in a homoeologous region of
another genus.
Klug, W.S., and M.R. Cummings. 1996. Essentials of genetics,
2nd edn. Prentice Hall, Upper Saddle, NJ.
Klug, W.S., and M.R. Cummings. 1997. Concepts of genetics,
5th edn. Prentice Hall, Upper Saddle, NJ.
Stahl, F.W. 1979. Genetic recombination. Sci. Am. 256:91–101.
Weinberg, R.A. 1985. The molecules of life. Sci. Am.
253:48–57.